Note: This page contains sample records for the topic acceleration exposure limit from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Voltage limitations of electrostatic accelerators  

SciTech Connect

The history of electrostatic accelerators has been punctuated by a series of projects in which innovative designs have failed to meet the expectations of their designers. From the early, air-insulated Van de Graaffs at Round Hill to certain of the large pressurized heavy ion accelerators of the 1970s and 1980s, increases in size or changes in design and materials have not always led to the maximum voltages expected or extrapolated. Since these failures have continued beyond childhood into a mature technology, it is reasonable to assume that the causes of voltage limitation are varied and complex. They have remained poorly understood for a number of reasons: resources for an extended program of research into breakdown and failure of electrostatic generators have always been meager, especially for large machines devoted to nuclear research; the inaccessibility of pressurized generators makes instrumentation difficult and testing slow; the calculation of transient and dynamic effects is laborious and the results difficult to verify; voltage test experiments on operating accelerators are inhibited by the significant risk of damage due to energy release on breakdown: and the total voltages (though not the local fields) achieved in many electrostatic accelerators exceed those produced in any other man-made environment. In this review, the behavior of several generators of different designs is examined in order to assess the importance of the various design features and operating conditions that control the maximum voltage achievable in a working machine. [copyright] [ital 1999 American Institute of Physics.

Hyder, H.R. (A. W. Wright Nuclear Structure Laboratory, Yale University P.O. Box 208124, New Haven, Connecticut 06520-8124 (United States))

1999-04-01

2

Voltage limitations of electrostatic accelerators  

SciTech Connect

The history of electrostatic accelerators has been punctuated by a series of projects in which innovative designs have failed to meet the expectations of their designers. From the early, air-insulated Van de Graaffs at Round Hill to certain of the large pressurized heavy ion accelerators of the 1970s and 1980s, increases in size or changes in design and materials have not always led to the maximum voltages expected or extrapolated. Since these failures have continued beyond childhood into a mature technology, it is reasonable to assume that the causes of voltage limitation are varied and complex. They have remained poorly understood for a number of reasons: resources for an extended program of research into breakdown and failure of electrostatic generators have always been meager, especially for large machines devoted to nuclear research; the inaccessibility of pressurized generators makes instrumentation difficult and testing slow; the calculation of transient and dynamic effects is laborious and the results difficult to verify; voltage test experiments on operating accelerators are inhibited by the significant risk of damage due to energy release on breakdown: and the total voltages (though not the local fields) achieved in many electrostatic accelerators exceed those produced in any other man-made environment. In this review, the behavior of several generators of different designs is examined in order to assess the importance of the various design features and operating conditions that control the maximum voltage achievable in a working machine.

Hyder, H. R. McK. [A. W. Wright Nuclear Structure Laboratory, Yale University P.O. Box 208124, New Haven, Connecticut 06520-8124 (United States)

1999-04-26

3

Voltage limitations of electrostatic accelerators  

NASA Astrophysics Data System (ADS)

The history of electrostatic accelerators has been punctuated by a series of projects in which innovative designs have failed to meet the expectations of their designers. From the early, air-insulated Van de Graaffs at Round Hill to certain of the large pressurized heavy ion accelerators of the 1970s and 1980s, increases in size or changes in design and materials have not always led to the maximum voltages expected or extrapolated. Since these failures have continued beyond childhood into a mature technology, it is reasonable to assume that the causes of voltage limitation are varied and complex. They have remained poorly understood for a number of reasons: resources for an extended program of research into breakdown and failure of electrostatic generators have always been meager, especially for large machines devoted to nuclear research; the inaccessibility of pressurized generators makes instrumentation difficult and testing slow; the calculation of transient and dynamic effects is laborious and the results difficult to verify; voltage test experiments on operating accelerators are inhibited by the significant risk of damage due to energy release on breakdown: and the total voltages (though not the local fields) achieved in many electrostatic accelerators exceed those produced in any other man-made environment. In this review, the behavior of several generators of different designs is examined in order to assess the importance of the various design features and operating conditions that control the maximum voltage achievable in a working machine.

Hyder, H. R. Mck.

1999-04-01

4

Concussion. Acceleration limits causing concussion.  

PubMed

Among the many features common to all species of the animal kingdom is the transient loss of function of the nervous system as the result of a jarring blow, a phenomenon known as concussion. Understanding of concussion has been hampered by the lack of a uniform definition, with many authors including cases with gross, irreversible changes. The phenomenon occurs only with a blow that significantly accelerates and thus is best defined as "a transient disturbance of neuronal function as a result of acceleration." There must be a threshold beneath which no loss of function occurs and a ceiling beyond which changes are not reversible. Experiments with nonanesthetized frogs revealed that at 33 g only the occasional frog would be stunned. From 50 to 230 g, consciousness was always lost but rapidly regained and retained, while beyond, the loss was not always reversible. The time of functional loss was increasingly proportional to acceleration. PMID:3261046

Parkinson, D; Jell, R M

1988-08-01

5

Power balance limit in collective ion acceleration  

Microsoft Academic Search

The power balance limit to the IREB beam front propagation velocity, as first applied to the problem of collective ion acceleration by Olson in 1973, is investigated in view of recent data of Ecker and Putnam. The beam front velocity ..beta..\\/sub f\\/c as a function of IREB impedance Z is given, showing the dependence on the power balance limit, the

1978-01-01

6

Count rate limitations in pulsed accelerator fields  

SciTech Connect

This paper discusses various concepts involved in the counting losses of pulse-counting health physics instrumentation when used within the pulsed radiation environments of typical accelerator fields, in order to pre-establish appropriate limitations in use. Discussed are the 'narrow' pulse and the 'wide' pulse cases, the special effect of neutron moderating assemblies, and the effect of pulse microstructure on the counting losses of the pulse-counting instrumentation. Examples are provided which highlight the various concepts and limitations.

Justus, Alan L [Los Alamos National Laboratory

2010-12-15

7

Ultra-accelerated natural sunlight exposure testing  

SciTech Connect

Process and apparatus are disclosed for providing ultra accelerated natural sunlight exposure testing of samples under controlled weathering without introducing unrealistic failure mechanisms in exposed materials and without breaking reciprocity relationships between flux exposure levels and cumulative dose that includes multiple concurrent levels of temperature and relative humidity at high levels of natural sunlight comprising: (a) concentrating solar flux uniformly; (b) directing the controlled uniform sunlight onto sample materials in a chamber enclosing multiple concurrent levels of temperature and relative humidity to allow the sample materials to be subjected to accelerated irradiance exposure factors for a sufficient period of time in days to provide a corresponding time of about at least a years worth of representative weathering of the sample materials.

Jorgensen, G.J.; Bingham, C.; Goggin, R.; Lewandowski, A.A.; Netter, J.C.

2000-06-13

8

Space-charge limits in linear accelerators  

SciTech Connect

This report presents equations that allow an approximate evaluation of the limiting beam current for a large class of radio-frequency linear accelerators, which use quadrupole strong focusing. Included are the Alvarez, the Wideroe, and the radio-frequency quadrupole linacs. The limiting-current formulas are presented for both the longitudinal and the transverse degrees of freedom by assuming that the average space-charge force in the beam bunch arises from a uniformly distributed charge within an azimuthally symmetric three-dimensional ellipsoid. The Mathieu equation is obtained as an approximate, but general, form for the transverse equation of motion. The smooth-approximation method is used to obtain a solution and an expression for the transverse current limit. The form of the current-limit formulas for different linac constraints is discussed.

Wangler, T.P.

1980-12-01

9

LIMITS OF Nb3Sn ACCELERATOR MAGNETS  

SciTech Connect

Pushing accelerator magnets beyond 10 T holds a promise of future upgrades to machines like the Tevatron at Fermilab and the LHC at CERN. Exceeding the current density limits of NbTi superconductor, Nb{sub 3}Sn is at present the only practical superconductor capable of generating fields beyond 10 T. Several Nb{sub 3}Sn pilot magnets, with fields as high as 16 T, have been built and tested, paving the way for future attempts at fields approaching 20 T. High current density conductor is required to generate high fields with reduced conductor volume. However this significantly increases the Lorentz force and stress. Future designs of coils and structures will require managing stresses of several 100's of MPa and forces of 10's of MN/m. The combined engineering requirements on size and cost of accelerator magnets will involve magnet technology that diverges from the one currently used with NbTi conductor. In this paper we shall address how far the engineering of high field magnets can be pushed, and what are the issues and limitations before such magnets can be used in particle accelerators.

Caspi, Shlomo; Ferracin, Paolo

2005-05-01

10

Derivation of temporary emergency exposure limits (TEELs)  

Microsoft Academic Search

Short-term chemical concentration limits are used in a variety of applications, including emergency planning and response, hazard assessment and safety analysis. Development of emergency response planning guidelines (ERPGs) and acute exposure guidance levels (AEGLs) are predicated on this need. Unfortunately, the development of peer-reviewed community exposure limits for emergency planning cannot be done rapidly (relatively few ERPGs or AEGLs are

Douglas K. Craig; Janet S. Davis; Doan J. Hansen; Achille J. Petrocchi; T. Jordan Powell; Thomas E. Tuccinardi

2000-01-01

11

Toward WHO-recommended occupational exposure limits  

Microsoft Academic Search

The WHO Project on Recommended Health-based Limits in Occupational Exposure resulted in the development of occupational exposure limit (OEL) values for a few groups of widely used industrial chemicals. A comparative analysis of the WHO-recommended OEL and existing OEL in selected countries has been made. It was shown that in the OEL's development, there is need for harmonization of methodology,

M. I. Mikheev

1995-01-01

12

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing.  

National Technical Information Service (NTIS)

Evaluation of metal-based structures has long relied on atmospheric exposure test sites to determine corrosion resistance in marine environments. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating sa...

E. L. Montgomery J. C. Curran L. M. Calle M. R. Kolody

2011-01-01

13

Improving tritium exposure reconstructions using accelerator mass spectrometry  

PubMed Central

Direct measurement of tritium atoms by accelerator mass spectrometry (AMS) enables rapid low-activity tritium measurements from milligram-sized samples and permits greater ease of sample collection, faster throughput, and increased spatial and/or temporal resolution. Because existing methodologies for quantifying tritium have some significant limitations, the development of tritium AMS has allowed improvements in reconstructing tritium exposure concentrations from environmental measurements and provides an important additional tool in assessing the temporal and spatial distribution of chronic exposure. Tritium exposure reconstructions using AMS were previously demonstrated for a tree growing on known levels of tritiated water and for trees exposed to atmospheric releases of tritiated water vapor. In these analyses, tritium levels were measured from milligram-sized samples with sample preparation times of a few days. Hundreds of samples were analyzed within a few months of sample collection and resulted in the reconstruction of spatial and temporal exposure from tritium releases. Although the current quantification limit of tritium AMS is not adequate to determine natural environmental variations in tritium concentrations, it is expected to be sufficient for studies assessing possible health effects from chronic environmental tritium exposure.

Hunt, J. R.; Vogel, J. S.; Knezovich, J. P.

2010-01-01

14

Pitch then power: limitations to acceleration in quadrupeds  

PubMed Central

Rapid acceleration and deceleration are vital for survival in many predator and prey animals and are important attributes of animal and human athletes. Adaptations for acceleration and deceleration are therefore likely to experience strong selective pressures—both natural and artificial. Here, we explore the mechanical and physiological constraints to acceleration. We examined two elite athletes bred and trained for acceleration performance (polo ponies and racing greyhounds), when performing maximal acceleration (and deceleration for ponies) in a competitive setting. We show that maximum acceleration and deceleration ability may be accounted for by two simple limits, one mechanical and one physiological. At low speed, acceleration and deceleration may be limited by the geometric constraints of avoiding net nose-up or tail-up pitching, respectively. At higher speeds, muscle power appears to limit acceleration.

Williams, Sarah B.; Tan, Huiling; Usherwood, James R.; Wilson, Alan M.

2009-01-01

15

Radiation exposure limits for Japanese astronauts.  

PubMed

Starting in 2001, Japanese astronauts will live aboard the International Space Station (ISS) for 3 to 6 months a year. For astronauts, space radiation is primarily hazardous. Therefore, the National Space Development Agency of Japan (NASDA) is developing a system for Space Radiation Safety Operations. This report describes our overall image of Space Radiation Safety Operations aboard the ISS, especially our proceedings in drafting the "Space Radiation Exposure Limits for Japanese ISS Astronauts." PMID:10631331

Abe, T; Komiyama, T; Suemitsu, T

1999-12-01

16

47 CFR 1.1310 - Radiofrequency radiation exposure limits.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Radiofrequency radiation exposure limits. 1.1310 Section...of 1969 § 1.1310 Radiofrequency radiation exposure limits. The criteria listed...human exposure to radiofrequency (RF) radiation as specified in §...

2012-10-01

17

Exposure of Polymeric Glazing Materials Using NREL's Ultra-Accelerated Weathering System (UAWS)  

SciTech Connect

NREL's Ultra-Accelerated Weathering System (UAWS) selectively reflects and concentrates natural sunlight ultraviolet irradiance below 475 nm onto exposed samples to provide accelerated weathering of materials while keeping samples within realistic temperature limits. This paper will explain the design and implementation of the UAWS which allow it to simulate the effect of years of weathering in weeks of exposure. Exposure chamber design and instrumentation will be discussed for both a prototype UAWS used to test glazing samples as well as a commercial version of UAWS. Candidate polymeric glazing materials have been subjected to accelerated exposure testing at a light intensity level of up to 50 UV suns for an equivalent outdoor exposure in Miami, FL exceeding 15 years. Samples include an impact modified acrylic, fiberglass, and polycarbonate having several thin UV-screening coatings. Concurrent exposure is carried out for identical sample sets at two different temperatures to allow thermal effects to be quantified along with resistance to UV.

Bingham, C.; Jorgensen, G.; Wylie, A.

2010-01-01

18

Pushing the Limits of Accelerator Mass Spectrometry  

SciTech Connect

A renewed interest in Accelerator Mass Spectrometry (AMS) from nuclear physics laboratories is emerging in connection with Radioactive Ion Beams (RIBs). At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL) we are exploring the AMS capabilities of the 25-MV Tandem acclerator. Behind this effort is the realization that two fields of research - AMS and RIBs - complement each other in techniques. Development of effective and efficient beam purification techniques is of common interest to both AMS and the RIB program. Two main characteristics of the 25-MV Tandem provide unique opportunities for performing the highest sensitivity measurements of AMS; namely i) the highest operating voltage in the world, and ii) a folded geometry which involves a 180 degree magnet in the terminal. For the RIB program, we have used AMS techniques to improve the sensitivity of detection of some radioactive species in the measurement of unknown massses of n-rich nuclei. For AMS, we have concentrated in exploring two important isotopes, 14C and 36Cl, for applications that require the highest sensitivity. We have successfully measured 36Cl/Cl ratios as low as a few times 10-16 in seawater samples demonstrating that our set has the highest sensitivity for this isotope and proving that 36Cl can be measured at the levels required for a tracer in oceanography.

Galindo-Uribarri, Alfredo {nmn} [ORNL; Beene, James R [ORNL; Danchev, M. [University of Tennessee, Knoxville (UTK); Doupe, J. [University of Toronto; Fuentes Madariaga, Beatriz E [ORNL; Gomez Del Campo, Jorge [ORNL; Hausladen, Paul [ORNL; Juras, Raymond C [ORNL; Liang, J Felix [ORNL; Litherland, Albert E [ORNL; Liu, Yuan [ORNL; Meigs, Martha J [ORNL; Mills, Gerald D [ORNL; Mueller, Paul Edward [ORNL; Padilla-Rodal, Elizabeth [ORNL; Pavan, John R [ORNL; Sinclair IV, John W [ORNL; Stracener, Daniel W [ORNL

2007-01-01

19

Nondiffracting accelerating wave packets beyond the paraxial limit  

NASA Astrophysics Data System (ADS)

Self-accelerating Airy wave packets have stimulated rapidly growing research interest in the past five years. However, optical Airy beams are inherently subjected to the paraxial limit. Here, we demonstrate both theoretically and experimentally linear and nonlinear self-accelerating beams propagating along circular trajectories beyond the paraxial approximation. Such nonparaxial accelerating beams are exact solutions of the Helmholtz equation. Furthermore, we introduce and demonstrate nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of all previously found accelerating wave packets. We show that such beams bend into large angles along elliptical or parabolic trajectories but still retain nondiffracting and self-healing capabilities. The circular nonparaxial accelerating beams can be considered as a special case of the Mathieu accelerating beams, while an Airy beam is only a special case of the Weber beams at the paraxial limit. Not only do generalized nonparaxial accelerating wave packets open up many possibilities of beam engineering for applications, but the fundamental concept developed here can be applied to other linear wave systems in nature, ranging from electromagnetic and elastic waves to matter waves.

Zhang, Peng; Hu, Yi; Li, Tongcang; Cannan, Drake; Yin, Xiaobo; Morandotti, Roberto; Chen, Zhigang; Zhang, Xiang

2013-03-01

20

Accelerated Test for Filter Media Exposure to Fluoride Environment.  

National Technical Information Service (NTIS)

A simple dip test was devised using 1 wt % HF solution to establish an accelerated test which gives similar information on increase and decrease in tensile strength to that displayed in the exposures in the dynamic test system. Herty Sample Nos. 53, 54, a...

G. S. Petit F. N. Wiggins C. W. Weber

1977-01-01

21

Accelerated test for filter media exposure to fluoride environment  

Microsoft Academic Search

A simple dip test was devised using 1 wt % HF solution to establish an accelerated test which gives similar information on increase and decrease in tensile strength to that displayed in the exposures in the dynamic test system. Herty Sample Nos. 53, 54, and 56 contained only asbestos and L-134 fibers; their unexposed tensile strength ranged from 60 to

G. S. Petit; F. N. Wiggins; C. W. Weber

1977-01-01

22

Gradient limitations in room temperature and superconducting acceleration structures  

SciTech Connect

Accelerating gradient is a key parameter of the accelerating structure in large linac facilities, like future Linear Collider. In room temperature accelerating structures the gradient is limited mostly by breakdown phenomena, caused by high surface electric fields or pulse surface heating. High power processing is a necessary procedure to clean surface and improve the gradient. In the best tested X-band structures the achieved gradient is exceed 100 MV/m in of {approx}200 ns pulses for breakdown rate of {approx} 10{sup -7}. Gradient limit depends on number of factors and no one theory which can explain all sets of experimental results and predict gradient in new accelerating structure. In paper we briefly overview the recent experimental results of breakdown studies, progress in understanding of gradient limitations and scaling laws. Although superconducting rf technology has been adopted throughout the world for ILC, it has frequently been difficult to reach the predicted performance in these structures due to a number of factors: multipactoring, field emission, Q-slope, thermal breakdown. In paper we are discussing all these phenomena and the ways to increase accelerating gradient in SC cavity, which are a part of worldwide R&D program.

Solyak, N.A.; /Fermilab

2008-10-01

23

Perceptual and oculomotor evidence of limitations on processing accelerating motion.  

PubMed

Psychophysical studies have demonstrated that humans are less sensitive to image acceleration than to image speed (e.g., Gottsdanker, 1956; Werkhoven, Snippe, & Toet, 1992). Because there is evidence that a common motion-processing stage subserves perception and pursuit (e.g., Watamaniuk & Heinen, 1999), either pursuit should be similarly impaired in discriminating acceleration or it must receive input from a system different from the one that processes visual motion for perception. We assessed the sensitivity of pursuit to acceleration or speed, and compared the results with those obtained in perceptual experiments done with similar stimuli and tasks. Specifically, observers pursued or made psychophysical judgments of targets that moved at randomly selected base speeds and subsequent accelerations. Oculomotor and psychophysical discrimination were compared by analyzing performance for the entire stimulus set sorted by either target acceleration or speed. Thresholds for pursuit and perception were higher for target acceleration than speed, further evidence that a common motion-processing stage limits the performance of both systems. PMID:14765954

Watamaniuk, Scott N J; Heinen, Stephen J

2003-11-21

24

Revised Airborne Exposure Limits for Chemical Warfare Agents  

Microsoft Academic Search

The Centers for Disease Control and Prevention (CDC) is revising airborne exposure limits (AELs) for tabun (GA), sarin (GB),\\u000a VX, and sulfur mustard (H, HT, and HD) for demilitarization workers and the general public. New exposure criteria include\\u000a short-term exposure limits (STELs) and immediately dangerous to life or health (IDLH) values. These new criteria augment revised\\u000a long-term criteria, which include

John A. Decker; Harvey W. Rogers

25

Enhanced laser ion acceleration from mass-limited foils  

SciTech Connect

This paper reports on simulations of solid mass-limited targets (MLT) via electrodynamic two-dimensional, three velocity component particle-in-cell simulations. The interaction with long (300 fs) high intensity (10{sup 20} W/cm{sup 2}) laser pulses with targets of diameter down to 1 {mu}m is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. Our results suggest that the most significant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.

Kluge, T.; Kraft, S. D.; Schramm, U.; Zeil, K.; Cowan, T. E.; Bussmann, M. [Forschungszentrum Dresden-Rossendorf e.V., D-01328 Dresden (Germany); Enghardt, W. [OncoRay-Center for Radiation Research in Oncology, Technische Universitaet Dresden, D-01307 Dresden (Germany)

2010-12-15

26

Occupational Exposure Limits For Novel Work Schedules  

Microsoft Academic Search

Work schedules other than 7 to 8?hr\\/day and 40?hr\\/week are being introduced in many industrial operations. Novel work schedules, such as four 10-hour workdays per week or three 12-hour workdays per week for three weeks followed by four 12-hour workdays for three weeks and several other plans are presently being used. The Threshold Limit Values (TLV) do not apply to

R. A. SCALA

1975-01-01

27

Neutron Exposure Accelerator System For Biological Effect Experiments (NASBEE)  

SciTech Connect

The neutron exposure accelerator system for biological effect experiments (NASBEE) was developed to study biological effects of fast neutrons. We have characterized the NASBEE neutron beams with neutron energy spectrum, absorbed dose energy distributions, and space distributions. The neutron energy spectrum shows 2.3 MeV as mean energy and 3.0 MeV as kerma of tissue-equivalent-plastic (A150) weighted mean energy, and the maximum neutron energy was determined to be 9 MeV. Neutron absorbed doses occupy 82% of the NASBEE neutron beam. NASBEE has been used to learn some of the outcomes of the biological effects of fast neutrons.

Takada, Masashi; Suda, Mitsuo; Kamada, So; Hagiwara, Takuya; Imaseki, Hitoshi; Hamano, Tsuyoshi [National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku Chiba, Japan 263-8555 (Japan)

2011-06-01

28

Health-based recommended occupational exposure limits for ethyl acrylate  

Microsoft Academic Search

The experimental no effect level was 20 mg ethyl acrylate\\/m3. The exposure with slight effects was at 100 mg\\/m3. The real no effect level is between 20 and 100 mg\\/m3. Therefore an occupational exposure limit of 20 mg eth-acr\\/m3 TWA 8 hr is advised with \\

M. A. Maclaine Pont

1990-01-01

29

10 CFR 850.22 - Permissible exposure limit.  

Code of Federal Regulations, 2013 CFR

...Section 850.22 Energy DEPARTMENT OF ENERGY CHRONIC BERYLLIUM DISEASE PREVENTION PROGRAM Specific Program Requirements...assure that no worker is exposed to an airborne concentration of beryllium greater than the permissible exposure limit established in...

2013-01-01

30

OSHA's permissible exposure limits: Regulatory compliance versus health risk  

Microsoft Academic Search

Workplace exposures to airborne chemicals are regulated in the U.S. by the Occupational Safety and Health Administration (OSHA) via the promulgation of permissible exposure limits (PELs). These limits, usually defined as eight-hour time-weighted average values, are enforced as concentrations never to be exceeded. In the case of chronic or delayed toxicants, the PEL is determined from epidemiological evidence and\\/or quantitative

Robert C. Spear; Steve Selvin

1989-01-01

31

Linking accelerated laboratory and outdoor exposure results for PV polymeric materials: a mechanistic study of EVA  

NASA Astrophysics Data System (ADS)

Linking accelerated laboratory test to field performance for predicting the service life of polymeric materials are being investigated at NIST using the reliability-based methodology. Based on this methodology, a successful linkage between the laboratory and field exposure data for a model polymeric material has been made. Recently, this methodology, for the first time, was introduced to the lifetime assessment of PV polymeric materials. In this paper, a mechanistic study of the degradation of three unstabilized model ethylene vinyl acetate (EVA) systems---uncured EVA, cured EVA and laminated EVA---was carried out under accelerated laboratory exposure and outdoor exposure. The NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was used for the accelerated laboratory tests, and the outdoor exposure was conducted in Gaithersburg, Maryland. Simultaneous multiple stresses, including temperature, relative humidity and UV radiation, were applied individually or in combination during SPHERE exposure. The effects of the environmental factors on the main degradation mechanisms of different EVA systems were investigated. The results showed that the UV radiation was the most important factor for the degradation of EVA and a synergistic effect occurred between UV radiation and relative humidity. A slower degradation rate was observed for the laminated system as a result of limited diffusion of O2 and H2O into EVA. It was also found that the substantial chemical changes of the uncured EVA system did not yield yellowing, which was dramatically different from the peroxide cured EVA system. Additionally, the chemical degradation modes of the three EVA systems exposed outdoors appeared to be similar to those exposed to the SPHERE. The implication of this work to the current test standards was discussed.

Gu, Xiaohong; Pang, Yongyan; Lin, Chiao-Chi; Liu, Kaipeng; Nguyen, Tinh; Chin, Jaonnie W.

2013-09-01

32

Lucky Exposures: Diffraction limited astronomical imaging through the atmosphere  

Microsoft Academic Search

Through selection of short exposure images we achieve diffraction-limited\\u000aI-band imaging from well-figured ground-based telescopes as large as 2.5 m\\u000adiameter. The faint limiting magnitude and large isoplanatic patch size for the\\u000aLucky Exposures technique at the Nordic Optical Telescope means that 25% of the\\u000anight sky is within range of a suitable reference star for I-band imaging.\\u000aTypically the

Robert Nigel Tubbs

2003-01-01

33

The development and regulation of occupational exposure limits in Taiwan  

Microsoft Academic Search

The occupational exposure limits (OELs) in Taiwan was promulgated in 1974 and has been revised five times since then. Many of the OELs were adopted from the most recent ACGIH TLVs and US OSHA PELs. A total of 483 chemicals were listed in the current Taiwan OELs Standard. The procedures of OELs development in Taiwan include the IOSH organized a

Tung-Sheng Shih; Kuen-Yuh Wu; Hong-I Chen; Cheng-Ping Chang; Ho-Yuan Chang; Yi-Shiao Huang; Saou-Hsing Liou

2006-01-01

34

Health-based recommended occupational exposure limits for halothane  

Microsoft Academic Search

The Dutch Expert Committee on Occupational Standards recommends a health-based occupational exposure limit (HBR-OEL) for halothane of 0.41 mg\\/m3 (0.05 ppm) as an eight-hour time-weighted average concentration.

M. A. Maclaine Pont

2002-01-01

35

Health-based recommended occupational exposure limit for dimethylamine  

Microsoft Academic Search

18 mg\\/m3 is an adverse effect level, causing minimal local (no systemic) effects in rats and mice. To take this into account a safety factor of 10 is applied which results in a recommended occupational exposure limit of 1.8 mg\\/m3 (1 ppm) TWA 8 h for DMA.

M. A. Maclaine Pont

1991-01-01

36

The Occupational Exposure Limit for Fluid Aerosol Generated in Metalworking Operations: Limitations and Recommendations  

PubMed Central

The aim of this review was to assess current knowledge related to the occupational exposure limit (OEL) for fluid aerosols including either mineral or chemical oil that are generated in metalworking operations, and to discuss whether their OEL can be appropriately used to prevent several health risks that may vary among metalworking fluid (MWF) types. The OEL (time-weighted average; 5 mg/m3, short-term exposure limit ; 15 mg/m3) has been applied to MWF aerosols without consideration of different fluid aerosol-size fractions. The OEL, is also based on the assumption that there are no significant differences in risk among fluid types, which may be contentious. Particularly, the health risks from exposure to water-soluble fluids may not have been sufficiently considered. Although adoption of The National Institute for Occupational Safety and Health's recommended exposure limit for MWF aerosol (0.5 mg/m3) would be an effective step towards minimizing and evaluating the upper respiratory irritation that may be caused by neat or diluted MWF, this would fail to address the hazards (e.g., asthma and hypersensitivity pneumonitis) caused by microbial contaminants generated only by the use of water-soluble fluids. The absence of an OEL for the water-soluble fluids used in approximately 80-90 % of all applicants may result in limitations of the protection from health risks caused by exposure to those fluids.

2012-01-01

37

Accelerated corrosion tests for aerospace materials: current limitations and future trends  

Microsoft Academic Search

Examines accelerated methods for the corrosion testing of materials, coatings and surface treatments used in the aerospace and defence industries. The drawbacks with some current accelerated corrosion tests are examined, particularly the problems experienced with neutral salt spray tests. Specific examples are given which identify the acute discrepancy between salt spray and marine exposure in the corrosion testing of metallic

K. R. Baldwin; C. J. E. Smith

1999-01-01

38

An overview of occupational benzene exposures and occupational exposure limits in Europe and North America.  

PubMed

Benzene has become one of the most intensely regulated substances in the world. Its ubiquitous use as a solvent has led to many working populations being exposed; in the early days often in uncontrolled conditions, leading to high exposures. Current occupational exposures are tightly controlled and are largely confined to workers in the petrochemical industry, vehicle mechanics, firefighters, workers exposed to automobile emissions, and some other occupational groups. Typically, occupational exposure levels are currently at or below 3.25 mg/m3 (1 ppm), and environmental exposures are typically below 50 microg/m3 (15 ppb). Smoking remains a significant source of exposure in both occupationally and non-occupationally exposed individuals. The early experiences of high occupational exposures led to the identification of haematopoietic effects of benzene and the need for improved control and regulation. As with most occupational standards, there has been a reduction in exposure limits as effects have been identified at ever-lower levels, accompanied by a societal concern for improved standards of occupational health. In 1946, the United States occupational exposure limit for benzene, promulgated by the American Conference of Governmental Industrial Hygienists, was 325 mg/m3 (100 ppm), but nowadays most European and North American countries have harmonised at 1.63-3.25mg/m3 (0.5-1 ppm). This latter figure was agreed within the European Union in 1997 and was adopted within national legislation by all Member States. The data on which this limit is set are essentially the same as those used by other standard-setting committees; this is an excellent example of how standards are set using science, pragmatism and societal values in the absence of complete information. PMID:15935799

Capleton, Alexander C; Levy, Leonard S

2005-04-18

39

Strategies for setting occupational exposure limits for particles.  

PubMed Central

To set occupational exposure limits (OELs) for aerosol particles, dusts, or chemicals, one has to evaluate whether mechanistic considerations permit identification of a no observed effect level (NOEL). In the case of carcinogenic effects, this can be assumed if no genotoxicity is involved, and exposure is considered safe if it does not exceed the NOEL. If tumor induction is associated with genotoxicity, any exposure is considered to be of risk, although a NOEL may be identified in the animal or human exposure studies. This must also be assumed when no information on the carcinogenic mechanism, including genotoxicity, is available. Aerosol particles, especially fibrous dusts, which include man-made mineral fiber(s) (MMMF), present a challenge for toxicological evaluation. Many MMMF that have been investigated have induced tumors in animals and genotoxicity in vitro. Since these effects have been associated with long-thin fiber geometry and high durability in vivo, all fibers meeting such criteria are considered carcinogenic unless the opposite has been demonstrated. This approach is practicable. Investigations on fiber tumorigenicity/genotoxicity should include information on dose response, pathobiochemistry, particle clearance, and persistence of the material in the target organ. Such information will introduce quantitative aspects into the qualitative approach that has so far been used to classify fibrous dusts as carcinogens. The rationales for classifying the potential carcinogenicity of MMMF and for setting OELs used by the different European committees and regulatory agencies are described.

Greim, H A; Ziegler-Skylakakis, K

1997-01-01

40

Considerations on accelerator systems requirements and limitations for ?-probe applications  

NASA Astrophysics Data System (ADS)

It is commonly accepted that the requirements for ?-probe applications on beam brightness and energy spread favour single-ended accelerators. With the Singletron™ systems HVE can offer high beam brightness (74 A m-2 rad-2 eV-1) and low energy spread as well as high terminal voltage stability (˜10 ppm). On the other hand, Tandetron™ systems have the advantage that no ion source maintenance is required in the tank as opposed to single-ended systems. Especially for the larger single-ended systems needed to obtain higher terminal voltages, source maintenance is time consuming. Tandem accelerators provide higher beam energies at the same terminal voltage. This offers the possibility of greater probe depths e.g. larger than 1 mm for protons (10 MeV) or over 300 ?m for He3 (15 MeV) in biological samples, which can be desired in single-cell irradiation experiments. Single-ended and tandem systems exhibit several important differences. First, of course the difference in ion sources, as for a tandem system a negative ion source is needed. The development of these sources has led to the availability of the multicusp ion source that combines low beam emittance with high current. Furthermore, related to the stripping process needed with a tandem accelerator, energy straggling of the ions increases the energy spread and small angle scattering of the ions tends to lower the beam brightness. At HVE, we investigated the influence of the small angle scattering on the beam brightness. Various ion optical approaches were compared and it was concluded that a multicusp ion source provides the possibility to minimise the degradation in the beam brightness due to small angle scattering of the ions. It is expected that a beam brightness of 10 50 A m-2 rad-2 eV-1 can be achieved with the Tandetron™ accelerator systems.

Visser, J.; Mous, D. J. W.; Gottdang, A.; Haitsma, R. G.

2005-04-01

41

Effects of Accelerated Exposure Testing (AET) Conditions on Performance Degradation of Solar Cells and Encapsulants  

SciTech Connect

The paper briefly summarizes the results from several accelerated exposure tests (AET) studies. Causes responsible for the photothermal instability of the encapsulated Si solar cells appear to be multiple and complex.

Glick, S. H.; Pern, F. J.

2000-01-01

42

Development of occupational exposure limits for the Hanford tank farms.  

PubMed

Production of plutonium for the United States' nuclear weapons program from the 1940s to the 1980s generated 53 million gallons of radioactive chemical waste, which is stored in 177 underground tanks at the Hanford site in southeastern Washington State. Recent attempts to begin the retrieval and treatment of these wastes require moving the waste to more modern tanks and result in potential exposure of the workers to unfamiliar odors emanating from headspace in the tanks. Given the unknown risks involved, workers were placed on supplied air respiratory protection. CH2MHILL, the managers of the Hanford site tank farms, asked an Independent Toxicology Panel (ITP) to assist them in issues relating to an industrial hygiene and risk assessment problem. The ITP was called upon to help determine the risk of exposure to vapors from the tanks, and in general develop a strategy for solution of the problem. This paper presents the methods used to determine the chemicals of potential concern (COPCs) and the resultant development of screening values and Acceptable Occupational Exposure Limits (AOELs) for these COPCs. A total of 1826 chemicals were inventoried and evaluated. Over 1500 chemicals were identified in the waste tanks headspaces and more than 600 of these were assigned screening values; 72 of these compounds were recommended for AOEL development. Included in this list of 72 were 57 COPCs identified by the ITP and of these 47 were subsequently assigned AOELs. An exhaustive exposure assessment strategy was developed by the CH2MHILL industrial hygiene department to evaluate these COPCs. PMID:20180654

Still, Kenneth R; Gardner, Donald E; Snyder, Robert; Anderson, Thomas J; Honeyman, James O; Timchalk, Charles

2010-04-01

43

47 CFR 1.1310 - Radiofrequency radiation exposure limits.  

Code of Federal Regulations, 2010 CFR

...radiofrequency (RF) radiation as specified...Guidelines for Human Exposure to Radiofrequency Radiation.â Note to...National Council on Radiation Protection and...Biological Effects and Exposure...Radiofrequency Electromagnetic Fields...with Respect to Human Exposure to...

2010-10-01

44

47 CFR 1.1310 - Radiofrequency radiation exposure limits.  

Code of Federal Regulations, 2010 CFR

...radiofrequency (RF) radiation as specified...Guidelines for Human Exposure to Radiofrequency Radiation.â Note to...National Council on Radiation Protection and...Biological Effects and Exposure...Radiofrequency Electromagnetic Fields...with Respect to Human Exposure to...

2009-10-01

45

Adjusting Exposure Limits for Long and Short Exposure Periods Using A Physiological Pharmacokinetic Model  

Microsoft Academic Search

The rationale for adjusting occupational exposure limits for unusual work schedules is to assure, as much as possible, that persons on these schedules are placed at no greater risk of injury or discomfort than persons who work a standard 8?hr\\/day, 40?hr\\/week. For most systemic toxicants, the risk index upon which the adjustments are made will be either peak blood concentration

MELVIN E. ANDERSEN; MICHAEL G. MacNAUGHTON; HARVEY J. CLEWELL III; DENNIS J. PAUSTENBACH

1987-01-01

46

Establishment of occupational exposure limit for warfarin in China.  

PubMed

This study aims to establish the occupational exposure limit (OEL) in the air for workplace of warfarin based on the available toxicological studies and field investigations by using questionnaire and air monitoring. The clinical therapeutic dose was used as lowest observed effect level (LOEL), and no observed effect level (NOEL) was achieved by using a safety factor. The highest concentration of warfarin monitored in the worksite of centrifuge washing, drying and packing were 0.029 mg/m3, 0.051 mg/m3 respectively, which did not exceed the OEL 0.1 mg/m3 recommended by NIOSH and ACGIH. Considering its feasibility for enforcement and protection for workers, we recommend OEL 0.1 mg/m3 of warfarin in China. PMID:23816588

Xu, Jian Ning; Fu, Zhao Hui; Yu, Wen Lan; Wang, Quan Kai; Tan, Feng

2013-06-01

47

Accelerated corrosion exposure in ultra thin sheets of 2024 aircraft aluminium alloy for GLARE applications  

Microsoft Academic Search

The effect of corrosion exposure on ultra thin (t<0.4mm) 2024-T3 aluminium sheet thickness is investigated. Microstructural analysis showed that for low accelerated corrosion exposure times, no surface deterioration existed and hence corresponding mechanical properties degradation was assumed to be incited by hydrogen diffusion and subsequent embrittlement. Medium exposure times resulted in cross-section reduction due to formation of sub-surface corrosion products,

N. D. Alexopoulos; Ch. Dalakouras; P. Skarvelis; S. K. Kourkoulis

48

Limiting electron beam current for cyclic induction acceleration in a constant guide field  

SciTech Connect

Theoretical relations are derived for the limiting beam current in a cyclic induction accelerator (CIA) with a constant guide field. The calculations are in agreement with the available experimental data. It is shown that the limiting average beam current in a CIA is of the order of 100 microamperes, i.e., the level attained in microtrons and linear accelerators. The CIA may find industrial applications.

Kanunnikov, V.N.

1982-09-01

49

EIS studies of coated metals in accelerated exposure  

Microsoft Academic Search

One of the most popular uses of electrochemical impedance spectroscopy (EIS) is the characterization of the protective properties of coatings on corrodible metals. From early studies up to the present time, many EIS studies have been devoted to the study of the changes in the impedance of coated metals as they undergo either natural or artificial exposure to conditions that

Gordon Bierwagen; Dennis Tallman; Junping Li; Lingyun He; Carol Jeffcoate

2003-01-01

50

A recommended occupational exposure limit for formaldehyde based on irritation.  

PubMed

In recent years, several regulatory agencies and professional societies have recommended an occupational exposure limit (OEL) for formaldehyde. This article presents the findings of a panel of experts, the Industrial Health Foundation panel, who were charged to identify an OEL that would prevent irritation. To accomplish this task, they critiqued approximately 150 scientific articles. Unlike many other chemicals, a large amount of data is available upon which to base a concentration-response relationship for human irritation. A mathematical model developed by Kane et al. (1979) for predicting safe levels of exposure to irritants based on animal data was also evaluated. The panel concluded that for most persons, eye irritation clearly due to formaldehyde does not occur until at least 1.0 ppm. Information from controlled studies involving volunteers indicated that moderate to severe eye, nose, and throat irritation does not occur for most persons until airborne concentrations exceed 2.0-3.0 ppm. The data indicated that below 1.0 ppm, if irritation occurs in some persons, the effects rapidly subside due to "accommodation." Based on the weight of evidence from published studies, the panel found that persons exposed to 0.3 ppm for 4-6 h in chamber studies generally reported eye irritation at a rate no different than that observed when persons were exposed to clean air. It was noted that at a concentration of 0.5 ppm (8-h TWA) eye irritation was not observed in the majority of workers (about 80%). Consequently, the panel recommended an OEL of 0.3 ppm as an 8-h time-weighted average (TWA) with a ceiling value (CV) of 1.0 ppm (a concentration not to be exceeded) to avoid irritation. The panel believes that the ACGIH TLV of 0.3 ppm as a ceiling value was unnecessarily restrictive and that this value may have been based on the TLV Committee's interpretation of the significance of studies involving self-reported responses at concentrations less than 0.5 ppm. The panel concluded that any occupational or environmental guideline for formaldehyde should be based primarily on controlled studies in humans, since nearly all other studies are compromised by the presence of other contaminants. The panel also concluded that if concentrations of formaldehyde are kept below 0.1 ppm in the indoor environment (where exposures might occur 24 h/d) this should prevent irritation in virtually all persons. The panel could not identify a group of persons who were hypersensitive, nor was there evidence that anyone could be sensitized (develop an allergy) following inhalation exposure to formaldehyde. The panel concluded that there was sufficient evidence to show that persons with asthma respond no differently than healthy individuals following exposure to concentrations up to 3.0 ppm. Although cancer risk was not a topic that received exhaustive evaluation, the panel agreed with other scientific groups who have concluded that the cancer risk of formaldehyde is negligible at airborne concentrations that do not produce chronic irritation. PMID:9055874

Paustenbach, D; Alarie, Y; Kulle, T; Schachter, N; Smith, R; Swenberg, J; Witschi, H; Horowitz, S B

1997-02-21

51

Limits of fetal thyroid risk from radioiodine exposure  

SciTech Connect

An incident in which a young women became pregnant soon after being treated with 444 MBq {sup 131}I for Graves disease prompted us to search local records for the occurrence of thyroid abnormalities among people exposed in utero to fallout radioiodine. The data base from the Utah Fallout Study indicated that there had been 480 cohort subjects for whom dose to thyroid from fallout radioiodine had been calculated and who could have received any thyroid dose before birth (2473 subjects had been re-examined in 1985-86 of the 4818 examined in 1965-70). Of these 480 subjects in this category, 403 of them could be located in the 1980`s and were examined for abnormalities. Although nodules, thyroiditis, hypothyroidism and goiter were seen among the 375 persons with in utero thyroid doses from fallout radioiodine below 0.42 Gy, no thyroid abnormalities of any kind occurred in the 4 persons with in utero thyroid doses of 0.5 to 2.6 Gy. In addition, no neoplasia was found in any of the 403 subjects examined about 3 decades after in utero fallout exposure. These limited data do not indicate that the fetal thyroid is more sensitive than the postnatal thyroid by more than about a factor of about 4 when thyroid dose is considered and by not much more than unity when the comparison is based on dose equivalent (x-ray vs. radioiodine). 21 refs., 1 tab.

Lloyd, R.D.; Tripp, D.A.; Kerber, R.A. [Univ. of Utah School of Medicine, Salt Lake City, UT (United States)

1996-04-01

52

Health-based recommended occupational exposure limits for phthalic anhydride  

Microsoft Academic Search

As inhalation is the most likely route of exposure the proposed MAC-value is based on an evaluation of the inhalatory data in man and animals. The earliest appearing effect after prolonged exposure of experimental animals (3 hr\\/day on 4 consecutive days, followed by 10 days without exposure, during 8 months) to 8.5 mg PAN\\/m3 was hyperaemia of the mucous membrane

M. A. Maclaine Pont

1989-01-01

53

Adaptive parametric interpolation scheme with limited acceleration and jerk values for NC machining  

Microsoft Academic Search

Parametric interpolation has many advantages over the traditional linear or circular interpolation in computer numerical control\\u000a (CNC) machining. The existing work in this regard is reported to have achieved constant feedrate, confined chord error and\\u000a limited acceleration\\/deceleration in one interpolator. However, the excessive jerk still exists due to abrupt change in acceleration\\u000a profile, which will cause shock to the machine

Rong Zhen Xu; Le Xie; Cong Xin Li; Dao Shan Du

2008-01-01

54

Laser-driven ion acceleration using isolated mass-limited spheres  

NASA Astrophysics Data System (ADS)

We report on our experiments on laser-driven ion acceleration using fully isolated mass-limited spheres with a diameter down to 8 ?m for the first time. Two-dimensional (2D) particle-in-cell (PIC) and hydro-code simulations were used to show that the pre-plasma at both the front and rear sides of the target strongly affect the efficiency of the ion acceleration. The mechanism of the plasma flow around mass-limited targets has not yet been identified for laser-driven ion acceleration. Our models indicate that this effect is the cause of the observed limitation to the ion-beam energy in both previous experiments and in our own.

Sokollik, T.; Paasch-Colberg, T.; Gorling, K.; Eichmann, U.; Schnürer, M.; Steinke, S.; Nickles, P. V.; Andreev, A.; Sandner, W.

2010-11-01

55

76 FR 60500 - Request for Information: Announcement of Carcinogen and Recommended Exposure Limit (REL) Policy...  

Federal Register 2010, 2011, 2012, 2013

...Director of the National Institute for Occupational Safety and Health (NIOSH) of the...carcinogens and establishing recommended exposure limits (RELs) for occupational exposures to hazards associated with cancer.'' As part of this effort,...

2011-09-29

56

An accelerated exposure and testing apparatus for building joint sealants  

NASA Astrophysics Data System (ADS)

The design, fabrication, and implementation of a computer-controlled exposure and testing apparatus for building joint sealants are described in this paper. This apparatus is unique in its ability to independently control and monitor temperature, relative humidity, ultraviolet (UV) radiation, and mechanical deformation. Each of these environmental factors can be controlled precisely over a wide range of conditions during periods of a month or more. Moreover, as controlled mechanical deformations can be generated, in situ mechanical characterization tests can be performed without removing specimens from the chamber. Temperature and humidity were controlled during our experiments via a precision temperature regulator and proportional mixing of dry and moisture-saturated air; while highly uniform UV radiation was attained by attaching the chamber to an integrating sphere-based radiation source. A computer-controlled stepper motor and a transmission system were used to provide precise movement control. The reliability and effectiveness of the apparatus were demonstrated on a model sealant material. The results clearly show that this apparatus provides an excellent platform to study the long-term durability of building joint sealants.

White, C. C.; Hunston, D. L.; Tan, K. T.; Hettenhouser, J.; Garver, J. D.

2013-09-01

57

An accelerated exposure and testing apparatus for building joint sealants.  

PubMed

The design, fabrication, and implementation of a computer-controlled exposure and testing apparatus for building joint sealants are described in this paper. This apparatus is unique in its ability to independently control and monitor temperature, relative humidity, ultraviolet (UV) radiation, and mechanical deformation. Each of these environmental factors can be controlled precisely over a wide range of conditions during periods of a month or more. Moreover, as controlled mechanical deformations can be generated, in situ mechanical characterization tests can be performed without removing specimens from the chamber. Temperature and humidity were controlled during our experiments via a precision temperature regulator and proportional mixing of dry and moisture-saturated air; while highly uniform UV radiation was attained by attaching the chamber to an integrating sphere-based radiation source. A computer-controlled stepper motor and a transmission system were used to provide precise movement control. The reliability and effectiveness of the apparatus were demonstrated on a model sealant material. The results clearly show that this apparatus provides an excellent platform to study the long-term durability of building joint sealants. PMID:24089872

White, C C; Hunston, D L; Tan, K T; Hettenhouser, J; Garver, J D

2013-09-01

58

Accelerating the Early Numeracy Development of Kindergartners with Limited Working Memory Skills through Remedial Education  

ERIC Educational Resources Information Center

Background: Young children with limited working memory skills are a special interest group among all children that score below average on early numeracy tests. This study examines the effect of accelerating the early numeracy development of these children through remedial education, by comparing them with children with typically working memory…

Toll, Sylke W. M.; Van Luit, Johannes E. H.

2013-01-01

59

30 CFR 57.5060 - Limit on exposure to diesel particulate matter.  

Code of Federal Regulations, 2013 CFR

...false Limit on exposure to diesel particulate matter. 57.5060 Section 57.5060 Mineral Resources...Radiation, Physical Agents, and Diesel Particulate Matter Diesel Particulate Matter-Underground Only § 57.5060 Limit on...

2013-07-01

60

30 CFR 57.5060 - Limit on exposure to diesel particulate matter.  

Code of Federal Regulations, 2010 CFR

...false Limit on exposure to diesel particulate matter. 57.5060 Section 57.5060 Mineral Resources...Radiation, Physical Agents, and Diesel Particulate Matter Diesel Particulate Matter-Underground Only § 57.5060 Limit on...

2010-07-01

61

30 CFR 57.5060 - Limit on exposure to diesel particulate matter.  

Code of Federal Regulations, 2010 CFR

...false Limit on exposure to diesel particulate matter. 57.5060 Section 57.5060 Mineral Resources...Radiation, Physical Agents, and Diesel Particulate Matter Diesel Particulate Matter-Underground Only § 57.5060 Limit on...

2009-07-01

62

Limited utility of Birkhoff's theorem in modified Newtonian dynamics: Nonzero accelerations inside a shell  

SciTech Connect

We investigate the consequences of Birkhoff's theorem in general relativity (GR) and in modified Newtonian dynamics (MOND). We study, in particular, the system of a finite-mass test particle inside a spherical shell. In both GR and MOND, we find nonvanishing acceleration for that test particle. The direction of the acceleration is such that it pushes the test particle toward the center of the shell. In GR, the acceleration is found analytically in the case of a small test mass with a small displacement from the center of the shell. In MOND, the acceleration is found analytically in the limit of large test mass and small displacement, and a comparison to numerical values is made. Numerical simulations are done for more general cases with parameters that mimic the system of a galaxy in a cluster. In GR, the acceleration is highly suppressed and physically insignificant. In MOND, on the contrary, the acceleration of the point particle can be a significant fraction of the field just outside of the spherical shell.

Dai Dechang [Department of Physics, SUNY at Buffalo, Buffalo, New York 14260-1500 (United States); Matsuo, Reijiro; Starkman, Glenn [CERCA, Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079 (United States)

2010-01-15

63

Analysis of biological effects and limits of exposure to weak magnetic fields  

Microsoft Academic Search

Adverse biological outcomes due to thermal effects of exposure to high power magnetic fields are well understood and are the basis for standards for limiting human exposure to such fields. Over the past few decades a controversy has arisen over possible adverse biological effects due to exposure to weak, low frequency magnetic fields. This paper involves a critical analysis of

D. A. Chathurika; M. F. Peter; N. H. Malka

2010-01-01

64

30 CFR 57.5001 - Exposure limits for airborne contaminants.  

Code of Federal Regulations, 2013 CFR

...exceeding the 0.1 f/cc full-shift limit or the 1 f/cc excursion limit, samples shall be further analyzed using transmission electron microscopy according to NIOSH Method 7402 or a method at least equivalent to that method. (c) Employees shall be...

2013-07-01

65

30 CFR 56.5001 - Exposure limits for airborne contaminants.  

Code of Federal Regulations, 2013 CFR

...exceeding the 0.1 f/cc full-shift limit or the 1 f/cc excursion limit, samples shall be further analyzed using transmission electron microscopy according to NIOSH Method 7402 or a method at least equivalent to that method. (c) Employees shall be...

2013-07-01

66

Vector instabilities and self-acceleration in the decoupling limit of massive gravity  

NASA Astrophysics Data System (ADS)

We investigate in detail the vector contributions to the Lagrangian of ?3 massive gravity in the decoupling limit, the less explored sector of this theory, with the main aim to study the stability of maximally symmetric self-accelerating solutions. Around self-accelerating configurations, vector degrees of freedom become strongly coupled since their kinetic terms vanish; their dynamics is controlled by contributions to the Lagrangian that arise at higher orders in perturbations. Even in the decoupling limit, the vector Lagrangian contains an infinite number of terms. We develop a systematic method to determine in a covariant way the vector Lagrangian at each order in perturbations, fully manifesting the symmetries of the system. We show that, around self-accelerating solutions, the structure of higher order p-form Galileons arise, avoiding the emergence of a sixth ghost Boulware-Deser mode. However, a careful analysis of the corresponding Hamiltonian shows that there are directions along which the Hamiltonian is unbounded from below, signaling an instability that can be interpreted as one of the available fifth modes behaving as a ghost. Hence, we conclude that self-accelerating configurations in the decoupling limit of ?3 massive gravity are generically unstable.

Tasinato, Gianmassimo; Koyama, Kazuya; Niz, Gustavo

2013-03-01

67

Health-based recommended occupational exposure limits for methyl acrylate  

Microsoft Academic Search

Me-acr can be absorbed totally after dermal, and oral exposure. Me-acr is metabolized fairly rapidly and elimination occurs for a large part via exhalation of CO2 and to a lesser extent via urinary excretion of thio-ethers. Me-acr is irritant to corrosive to the skin. Skin sensitization and cross sensitization to some of the related compounds occurs. In a two-year inhalatory

M. A. Maclaine Pont

1990-01-01

68

The effect of respiratory activity on brain blood flow during exposure to +Gz acceleration.  

PubMed

The effect of respiratory activity on cardiovascular system during the exposure to +Gz acceleration was studied. For simultaneous, beat to beat evaluation of central and global cerebral blood flow, the system based on modified impedance cardiography method was used. The mechanism of modulation of the central and peripheral (cerebral) venous pressures and blood flow by intrathoracic pressure changes, has been shown. The data obtained from these studies suggest that reconsideration of the respiration technique during Anti-GSM seems indispensable. PMID:11540262

Walichnowski, W; Kowalski, W; Bulski, W

1996-09-01

69

Acceleration and modulation of facial nerve regeneration by exposure to a moderate hypergravitic field  

NASA Astrophysics Data System (ADS)

Quantitative histological study revealed that regeneration of sectioned guinea pig facial nerve is accelerated by exposure to a moderate hypergravitic field of 1.6g. A two fold increase in rate of regeneration and in sprouting was observed. Scar tissue formation was significantly reduced in animals exposed to the hypergravitic field. The results confirm a previous study in which regeneration was evaluated clinically and by qualitative histology.

Rozenzweig, E.; Ishay, J. S.

70

Photothermal stability of encapsulated Si solar cells and encapsulation materials upon accelerated exposures  

Microsoft Academic Search

We have conducted a series of accelerated exposure test (AET) studies for various samples of crystalline-Si (c-Si) and amorphous-Si (a-Si) cells that were encapsulated with different superstrates, pottants, and substrates. Transmittance, fluorescence, color indices, impedance spectroscopy, laser optical beam induced current (OBIC), and light and dark current–voltage (I–V) measurements were used to characterize the samples. Nonuniform browning patterns of ethylene

F. J. Pern; S. H. Glick

2000-01-01

71

Exposure to light at night accelerates aging and spontaneous uterine carcinogenesis in female 129/Sv mice.  

PubMed

The effect of the constant illumination on the development of spontaneous tumors in female 129/Sv mice was investigated. Forty-six female 129/Sv mice starting from the age of 2 mo were kept under standard light/dark regimen [12 h light (70 lx):12 hr dark; LD, control group], and 46 of 129/Sv mice were kept under constant illumination (24 h a day, 2,500 lx, LL) from the age of 5 mo until to natural death. The exposure to the LL regimen significantly accelerated body weight gain, increased body temperature as well as acceleration of age-related disturbances in estrous function, followed by significant acceleration of the development of the spontaneous uterine tumors in female 129/Sv mice. Total tumor incidence as well as a total number of total or malignant tumors was similar in LL and LD group (p > 0.05). The mice from the LL groups survived less than those from the LD group (? ( 2) = 8.5; p = 0.00351, log-rank test). According to the estimated parameters of the Cox's regression model, constant light regimen increased the relative risk of death in female mice compared with the control (LD) group (p = 0.0041). The data demonstrate in the first time that the exposure to constant illumination was followed by the acceleration of aging and spontaneous uterine tumorigenesis in female 129/Sv mice. PMID:23656779

Popovich, Irina G; Zabezhinski, Mark A; Panchenko, Andrei V; Piskunova, Tatiana S; Semenchenko, Anna V; Tyndyk, Maragriata L; Yurova, Maria N; Anisimov, Vladimir N

2013-05-06

72

Performance Degradation of Encapsulated Monocrystalline-Si Solar Cells upon Accelerated Weathering Exposures: Preprint  

SciTech Connect

Presented at 2001 NCPV Program Review Meeting: Performed accelerated exposures to study performance reliability/materials degradation of encapsulated c-Si cells using weathering protocols in 2 weatherometers. We have performed accelerated exposures to study performance reliability and materials degradation of a total of forty-one 3-cm x 3-cm monocrystalline-Si (c-Si) solar cells that were variously encapsulated using accelerated weathering protocols in two weatherometers (WOMs), with and without front specimen water sprays. Laminated cells (EVA/c-Si/EVA, ethylene vinyl acetate) with one of five superstrate/substrate variations and other features including with and without: (i) load resistance, (ii) Al foil light masks, and (iii) epoxy edge-sealing were studied. Three additional samples, omitting EVA, were exposed under a full-spectrum solar simulator, or heated in an oven, for comparison. After exposures, cell performance decreased irregularly, but to a relatively greater extent for samples exposed in WOM where light, heat, and humidity cycles were present (solar simulator or oven lacked such cycles). EVA laminates in the samples masked with aluminum (Al) foils were observed to retain moisture in WOM with water spray. Moisture effects caused substantial efficiency losses probably related in part to increasing series resistance.

Glick, S. H.; Pern, F. J.; Watson, G. L.; Tomek, D.; Raaff, J.

2001-10-01

73

30 CFR 57.5001 - Exposure limits for airborne contaminants.  

Code of Federal Regulations, 2010 CFR

...Limit Values for Chemical Substances in Workroom Air Adopted by ACGIH for 1973,â pages 1 through 54, which are hereby incorporated...Customer Service, Cincinnati, OH 45240, http://www.acgih.org , or may be examined in any Metal and Nonmetal...

2010-07-01

74

30 CFR 56.5001 - Exposure limits for airborne contaminants.  

Code of Federal Regulations, 2010 CFR

...Limit Values for Chemical Substances in Workroom Air Adopted by ACGIH for 1973,â pages 1 through 54, which are hereby incorporated...Customer Service, Cincinnati, OH 45240; http://www.acgih.orgâ , or may be examined in any Metal and...

2010-07-01

75

30 CFR 57.5001 - Exposure limits for airborne contaminants.  

Code of Federal Regulations, 2010 CFR

...Limit Values for Chemical Substances in Workroom Air Adopted by ACGIH for 1973,â pages 1 through 54, which are hereby incorporated...Customer Service, Cincinnati, OH 45240, http://www.acgih.org , or may be examined in any Metal and Nonmetal...

2009-07-01

76

Accelerator mass spectrometry in the biomedical sciences: applications in low-exposure biomedical and environmental dosimetry  

NASA Astrophysics Data System (ADS)

We are utilizing accelerator mass spectrometry as a sensitive detector for tracking the disposition of radioisotopically labeled molecules in the biomedical sciences. These applications have shown the effectiveness of AMS as a tool to quantify biologically important molecules at extremely low levels. For example, AMS is being used to determine the amount of carcinogen covalently bound to animal DNA (DNA adduct) at levels relevent to human exposure. Detection sensitivities are 1 carcinogen molecule bound in 1011 to 1012 DNA bases, depending on the specific activity of the radiolabeled carcinogen. Studies have been undertaken in our laboratory utilizing heterocyclic amine food-borne carcinogens and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent environmental carcinogen, to study the metabolism of carcinogens at low doses. In addition, AMS is being used to detect the presence of rare proteins (mutant forms of protamine) in human sperm. Approximately l per 106 sperm analyzed contain the rare form of the protamine. Protamine isolated from this small number of cells is being analyzed by AMS, following 14C labeling. Thus, AMS can be used to verify the identity of an extremely small amount of biological material. Furthermore, an additional improvement of 2 orders of magnitude in the sensitivity of biomédical tracer studies is suggested by preliminary work with bacterial hosts depleted in radiocarbon. Other problems in the life sciences where detection sensitivity or sample sizes are limitations should also benefit from AMS. Studies are underway to measure the molecular targeting of cancer chemotherapeutics in human tissue and to pursue applications for receptor biology. We are also applying other candidate isotopes, such as 3H (double labeling with 14C) and 41Ca (bone absorption) to problems in biology. The detection of 36Cl and 26Al have applications for determination of human neutron exposure and understanding neurological toxicity, respectively. The results described here with 14C-labeled molecules coupled with new isotope applications clearly show AMS technology to be an important new tool for the biomedical sciences community.

Felton, J. S.; Turteltaub, K. W.; Vogel, J. S.; Balhorn, R.; Gledhill, B. L.; Southon, J. R.; Caffee, M. W.; Finkel, R. C.; Nelson, D. E.; Proctor, I. D.; Davis, J. C.

1990-12-01

77

Estimating the Mean, Variance, and Confidence Limits from Censored (<Limit of Detection), Lognormally-Distributed Exposure Data  

Microsoft Academic Search

A published statistical technique is applied to an exposure distribution having measurements that are less than the analytical limit of detection (LOD). The method uses the mean and standard deviation of known or quantitated values and the number of censored or nonquantitated (

JIMMY L. PERKINS; GARY N. CUTTER; MICHAEL S. CLEVELAND

1990-01-01

78

A new approach of studying correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials  

Microsoft Academic Search

The correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials was investigated\\u000a according to the variation of the functional group of exposure models aged. Environment aging intesities at different zones\\u000a (Wuhan and Lasa with the same latitude) and the influences of indoor accelerating factors including water and ultraviolet\\u000a on weathering performance of high polymer materials were

Yang Lixia; Li Xiaogang; Zhang Sanping

2006-01-01

79

Acceleration, beaming, and synchrotron radiation above the 160 MeV limit from relativistic pair reconnection  

NASA Astrophysics Data System (ADS)

Magnetic reconnection converts magnetic field energy into particle kinetic energy, accelerating particles to sufficient energies to emit gamma-ray synchrotron radiation in astrophysical contexts, possibly including pulsar wind nebulae, Gamma-Ray Bursts, and blazar jets. A balance between acceleration (by the electric field E) and synchrotron braking (while orbiting a B-field line) limits particle energy so that synchrotron processes cannot emit photons above about 160 MeV, unless E > B. However, short, intense gamma-ray flares of much higher energies have recently been observed in the Crab nebula. This work demonstrates, using 2D simulations, that reconnection in relativistic electron-positron pair plasmas can accelerate particles in Speiser orbits around the magnetic null (where E > B) such that the particles can emit synchrotron photons above the 160 MeV limit. Furthermore, reconnection bunches particles and focuses them into beams; high-energy synchrotron radiation is also strongly beamed, and the sweeping of the beam across the observer's line of sight can explain the fast time variability of the flares.

Werner, Gregory; Cerutti, Benoit; Uzdensky, Dmitri; Begelman, Mitchell

2013-04-01

80

Occupational exposure limits in Europe and Asia – Continued divergence or global harmonization?  

Microsoft Academic Search

Occupational exposure limits (OELs) are used as a risk management tool aiming at protecting against negative health effects of occupational exposure to harmful substances. The systems of OEL development have not been standardized and divergent outcomes have been reported. However some harmonization processes have been initiated, primarily in Europe. This study investigates the state of harmonization in a global context.

Qian Ding; Linda Schenk; Katarzyna Malkiewicz; Sven Ove Hansson

2011-01-01

81

Ethyl Methacrylate, n-butyl Methacrylate and Isobutyl Methacrylate: Health Based Recommended Occupational Exposure Limit.  

National Technical Information Service (NTIS)

Upon request by the Minister of Social Affairs and Employment the Health Council of the Netherlands recommends health-based occupational exposure limits for the concentration of toxic substances in air of the workplace. These recommendations are made by t...

1994-01-01

82

THE ACCELERATING ACTION OF ILLUMINATION IN RECOVERY OF ARBACIA EGGS FROM EXPOSURE TO ULTRAVIOLET RADIATION  

PubMed Central

Light of wave lengths 0.30µ to 0.50µ, accelerates return of the cleavage rate of Arbacia eggs to normal, after delay by exposure to ultraviolet radiation (wave lengths 0.238µ to 0.31µ). Recovery is apparently complete. Wave lengths 0.30µ to 0.50µ have no effect on the cleavage rate of normal eggs, nor does such illumination previous to dosage with ultraviolet radiation influence subsequent recovery. Acceleration of recovery of the egg occurs before fertilization as well as after. The effects of ultraviolet radiation and recovery therefrom are essentially the same in nucleated "white halves" as in the intact eggs. This phenomenon in the Arbacia egg seems basically comparable to photoreactivation of bacteria and fungi.

Blum, Harold F.; Loos, Gordon M.; Robinson, J. Courtland

1950-01-01

83

Review of the Evidence in Support of a Short Term Exposure Limit for Occupational Exposure to Ethylene Oxide.  

National Technical Information Service (NTIS)

Issues raised by the Office of Management and Budget (OMB) regarding the appropriateness of a short term exposure limit (STEL) for ethylene-oxide (75218) (EtO) were reviewed. Specific concerns addressed by the OMB were that OSHA had not quantified the red...

L. F. Mazzuckelli R. A. Lemen

1989-01-01

84

29 CFR Appendix A to Subpart Y of... - Examples of Conditions Which May Restrict or Limit Exposure to Hyperbaric Conditions  

Code of Federal Regulations, 2013 CFR

...Examples of Conditions Which May Restrict or Limit Exposure to Hyperbaric Conditions A Appendix A to Subpart Y of Part 1926 Labor...Examples of Conditions Which May Restrict or Limit Exposure to Hyperbaric Conditions Note: The requirements applicable to...

2013-07-01

85

The NREL Outdoor Accelerated-weathering Tracking System and Photovoltaic Module Exposure Results  

SciTech Connect

This paper describes the Outdoor Accelerated-weathering Tracking System (OATS) and interim results for the first OATS study on photovoltaic (PV) modules. With two test planes measuring 1.52 x 1.83 m, OATS provides a unique solar-concentrating exposure capability. Test sample temperatures are moderated by air blowers. Water spray capability exists for wetting samples. The OATS two-axis tracker points to the sun using software calculations. Non-imaging aluminum reflectors give a nominal clear-sky optical concentration ratio of three. Field-qualification measurements in the test plane under reflector conditions showed its relative irradiance non-uniformity was '' 15% for a clear-sky summer day with '' 75 mm as the smallest distance for that non-uniformity. Exposure studies began in November 1997 on seven pairs of commercially available ribbon silicon, crystalline silicon and amorphous silicon PV modules kept at constant resistive load. The modules were periodically removed from OATS for visual inspection and solar simulator performance measurements. There were no module failures. This PV module study is ongoing and later results will be compared to other testing techniques. Through July 1998, the modules under reflector conditions received 392 MJ/m2 of total ultraviolet (TUV) exposure. That was 2.07 times the TUV exposure compared to a south-facing fixed array tilted 40{sup o} up from horizontal at NREL. Similarly, the modules in the test plane under the covered reflectors received 1.04 times the fixed array TUV exposure. For the test plane under the covered reflectors there was a loss of 13% TUV exposure attributed to the reflectors blocking some of the diffuse-sky UV light. Also through July 1998, the OATS sunlight availability measured 95% compared to the cumulative global normal exposure at the NREL Solar Radiation Research Laboratory (SRRL). The OATS sunlight availability losses included downtime when the PV modules were removed, and when there were OAT S tracking problems, maintenance, and repair. For December 1997 through July 1998, the SRRL cumulative exposure was 99% compared to the respective monthly averages from years 1961 through 1990 at Boulder, Colorado.

Basso, T. S.

1998-10-31

86

Prenatal Exposure to Low Levels of Androgen Accelerates Female Puberty Onset and Reproductive Senescence in Mice  

PubMed Central

Sex steroid hormone production and feedback mechanisms are critical components of the hypothalamic-pituitary-gonadal (HPG) axis and regulate fetal development, puberty, fertility, and menopause. In female mammals, developmental exposure to excess androgens alters the development of the HPG axis and has pathophysiological effects on adult reproductive function. This study presents an in-depth reproductive analysis of a murine model of prenatal androgenization (PNA) in which females are exposed to a low dose of dihydrotestosterone during late prenatal development on embryonic d 16.5–18.5. We determined that PNA females had advanced pubertal onset and a delay in the time to first litter, compared with vehicle-treated controls. The PNA mice also had elevated testosterone, irregular estrous cyclicity, and advanced reproductive senescence. To assess the importance of the window of androgen exposure, dihydrotestosterone was administered to a separate cohort of female mice on postnatal d 21–23 [prepubertal androgenization (PPA)]. PPA significantly advanced the timing of pubertal onset, as observed by age of the vaginal opening, yet had no effects on testosterone or estrous cycling in adulthood. The absence of kisspeptin receptor in Kiss1r-null mice did not change the acceleration of puberty by the PNA and PPA paradigms, indicating that kisspeptin signaling is not required for androgens to advance puberty. Thus, prenatal, but not prepubertal, exposure to low levels of androgens disrupts normal reproductive function throughout life from puberty to reproductive senescence.

Witham, Emily A.; Meadows, Jason D.; Shojaei, Shadi; Kauffman, Alexander S.

2012-01-01

87

Acceleration  

Microsoft Academic Search

IN NATURE, NO. 1415, p. 125, Prof. Lodge asserts that the subject of acceleration is at the root of the perennial debate between engineers and teachers of mechanics; and he urges clearness of idea and accuracy of speech on all who deal with the junior student. Towards this end I would suggest that the too common phrase ``acceleration of velocity''

Edward Geoghegan

1897-01-01

88

Formate in serum and urine after controlled methanol exposure at the threshold limit value  

SciTech Connect

Methanol will be present as a new air pollutant when methanol-powered vehicles are introduced in the United States. Little is known about the effect of low-dose methanol exposure. It is controversial whether or not formate, the main metabolite responsible for methanol's acute toxicity, is a sensitive biological marker of toxicity or exposure. We studied the effect of a 4-hr exposure at rest to 200 ppm of methanol vapors on endogenous serum formate and on urinary formic acid excretion. A randomized, double-blind study of human exposure to a constant concentration of methanol was performed in a whole-body exposure chamber. Twenty-six healthy volunteers, each serving as his or her own control, participated in sham and methanol exposures. Urine (at 0, 4, 8 hr) and serum specimens (15 time points over 8 hr) collected before, during, and after the exposure were measured for formate. We found no significant differences in serum formate concentration between exposure and control conditions either at any time point or for area under the curve. Mean concentrations at the end of the exposure were: exposed 14.28 [+-] 8.90 mg/l and control 12.68 [+-] 6.43 mg/l. A slight, but nonsignificant (p = 0.08), increase in urine formate excretion rate was found at 4 hr (exposed 2.17 [+-] 1.69 mg/4 hr and control 1.67 [+-] 1.02 mg/4 hr). Age, sex, folic acid level, and smoking were not significant covariates. At 200 ppm, methanol exposure does not contribute substantially to endogenous formate quantities. Serum and urine formate determinations are not sensitive biological markers of methanol exposure at the threshold limit value. 24 refs., 4 tabs.

d'Alessandro, A. (Univ. of Perugia (Italy)); Osterloh, J.D.; Chuwers, P.; Quinlan, P.J.; Kelly, T.J.; Becker, C.E. (Univ. of California, San Francisco, CA (United States))

1994-02-01

89

A limited-memory acceleration strategy for MCMC sampling in hierarchical Bayesian calibration of hydrological models  

NASA Astrophysics Data System (ADS)

Hydrological calibration and prediction using conceptual models is affected by forcing/response data uncertainty and structural model error. The Bayesian Total Error Analysis methodology uses a hierarchical representation of individual sources of uncertainty. However, it is shown that standard multiblock "Metropolis-within-Gibbs" Markov chain Monte Carlo (MCMC) samplers commonly used in Bayesian hierarchical inference are exceedingly computationally expensive when applied to hydrologic models, which use recursive numerical solutions of coupled nonlinear differential equations to describe the evolution of catchment states such as soil and groundwater storages. This note develops a "limited-memory" algorithm for accelerating multiblock MCMC sampling from the posterior distributions of such models using low-dimensional jump distributions. The new algorithm exploits the decaying memory of hydrological systems to provide accurate tolerance-based approximations of traditional "full-memory" MCMC methods and is orders of magnitude more efficient than the latter.

Kuczera, George; Kavetski, Dmitri; Renard, Benjamin; Thyer, Mark

2010-07-01

90

Ion acceleration and anomalous transport in the near wake of a plasma limiter  

SciTech Connect

Ion acceleration and anomalous transport were studied experimentally in the near wake region of an electrically floating disk limiter immersed in two different types of collisionless, supersonically flowing, magnetized plasmas: the first initially quiescent, the second initially turbulent. Ion densities and velocity distributions were obtained using a nonperturbing laser induced fluorescence diagnostic. Large-amplitude, low-frequency turbulence was observed at the obstacle edge and in the wake. Rapid ion and electron configuration space transport and ion velocity space transport were observed. Configuration space and velocity space transport were similar for both quiescent and turbulent plasma-obstacle systems, suggesting that plasma-obstacle effects outweigh the effects of initial plasma turbulence levels. {copyright} {ital 1997 American Institute of Physics.}

Sheehan, D.P.; Bowles, J.; McWilliams, R. [Department of Physics and Astronomy, University of California, Irvine, California 92717 (United States)

1997-09-01

91

Specifications of a neutron exposure accelerator system for biological effects experiments (NASBEE) in NIRS  

NASA Astrophysics Data System (ADS)

We developed a neutron irradiation facility, neutron exposure accelerator system for biological effect experiments (NASBEE) for biological studies in National Institute of Radiological Sciences, Japan. Irradiation field of 2 MeV average neutrons generated by a Be(d-n)B reaction is established. Dose uniformity of 240 mm in diameter irradiation field is producible within ±2.5% with a dose rate of 0.87 Gy/h at sample target distance of 1170 mm. Two irradiation rooms, a specific pathogen-free (SPF) conditioned one and a conventional, are now available. Irradiation protocols for in vitro experiments are now established and demonstrated by obtaining a relative biological effectiveness (RBE) of cell inactivation measured to be 3.54 with 10% survival dose (D10).

Suda, Mitsuru; Hagihara, Takuya; Suya, Noriyoshi; Hamano, Tsuyoshi; Takada, Masashi; Konishi, Teruaki; Maeda, Takeshi; Ohmachi, Yasushi; Kakinuma, Shizuko; Ariyoshi, Kentaro; Shimada, Yoshiya; Imaseki, Hitoshi

2009-12-01

92

A Critical Appraisal of the Setting and Implementation of Occupational Exposure Limits in the Netherlands  

Microsoft Academic Search

Since 1978 in the Netherlands occupational exposure limits, designated maxi mum accepted concentrations (MACs), have been established by a three-step procedure. In the first, purely health-based, step the Dutch Expert Committee on Occupational Standards (DECOS), a committee of the Health Council of the Netherlands, establishes a health-based recommended occupational expo sure limit (HBR-OEL). In the second, feasibility, step the Subcommittee

V. J. Feron; C. Hoeksema; J. H. E. Artsa; P. C. Noordam; C. L. Maas

1994-01-01

93

Proposed Occupational Exposure Limits for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals  

SciTech Connect

A large number of volatile chemicals have been identified in the headspaces of tanks used to store mixed chemical and radioactive waste at the U.S. Department of Energy (DOE) Hanford Site, and there is concern that vapor releases from the tanks may be hazardous to workers. Contractually established occupational exposure limits (OELs) established by the Occupational Safety and Health Administration (OSHA) and American Conference of Governmental Industrial Hygienists (ACGIH) do not exist for all chemicals of interest. To address the need for worker exposure guidelines for those chemicals that lack OSHA or ACGIH OELs, a procedure for assigning Acceptable Occupational Exposure Limits (AOELs) for Hanford Site tank farm workers has been developed and applied to a selected group of 57 headspace chemicals.

Poet, Torka S.; Timchalk, Chuck

2006-03-24

94

Accelerated exposure tests of encapsulated Si solar cells and encapsulation materials  

SciTech Connect

We have conducted a series of accelerated exposure test (AET) studies for various crystalline-Si (c-Si) and amorphous-Si (a-Si) cell samples that were encapsulated with different superstrates, pottants, and substrates. Nonuniform browning patterns of ethylene vinyl acetate (EVA) pottants were observed for glass/EVA/glass-encapsulated c-Si cell samples under solar simulator exposures at elevated temperatures. The polymer/polymer-configured laminates with Tedlar or Tefzel did not discolor because of photobleaching reactions, but yellowed with polyester or nylon top films. Delamination was observed for the polyester/EVE layers on a-Si minimodules and for a polyolefin-based thermoplastic pottant at high temperatures. For all tested c-Si cell samples, irregular changes in the current-voltage parameters were observed that could not be accounted for simply by the transmittance changes of the superstrate/pottant layers. Silicone-type adhesives used under UV-transmitting polymer top films were observed to cause greater cell current/efficiency loss than EVA or polyethylene pottants. {copyright} {ital 1999 American Institute of Physics.}

Pern, F.J.; Glick, S.H. [Engineering and Reliability Division, National Center for Photovoltaics, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States)

1999-03-01

95

Proposed Occupational Exposure Limits for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals  

Microsoft Academic Search

A large number of volatile chemicals have been identified in the headspaces of tanks used to store mixed chemical and radioactive waste at the U.S. Department of Energy (DOE) Hanford Site, and there is concern that vapor releases from the tanks may be hazardous to workers. Contractually established occupational exposure limits (OELs) established by the Occupational Safety and Health Administration

Torka S. Poet; Chuck Timchalk

2006-01-01

96

A Proposed Approach for Setting Occupational Exposure Limits for Sensory Irritants Based on Chemosensory Models  

Microsoft Academic Search

Objectives: Setting occupational exposure limits (OELs) for odorous or irritating chemicals is a global occupational health challenge. However, often there is inadequate knowledge about the toxicology of these chemicals to set an OEL and their irritation potencies are usually not rec- ognized until they are manufactured or used in large quantities. Methods: In this paper, the importance of accounting for

SHANNON H. GAFFNEY; DENNIS J. PAUSTENBACH

2007-01-01

97

Approach to Setting Occupational Exposure Limits for Sensory Irritants in the Netherlands  

Microsoft Academic Search

This article describes how scientists in the Netherlands set occupational exposure limits (OELs) for sensory irritants. When they tackle this issue, a number of key questions need to be answered. For example, did the studies indeed measure sensory irritation and not cytotoxicity? When the irritant is an odorant, can interference of olfactory stimulation be excluded? In the case of subjective

V. J. Feron; J. H. E. Arts; J. Mojet

2001-01-01

98

Limiting Private Data Exposure in Online Transactions: A User-Based Online Privacy Assurance Model  

Microsoft Academic Search

Privacy conscious online shoppers find themselves forced to disseminate and share private data with new entities when engaging in online transactions. This paper provides a solution that limits private data exposure to entities that already have it. First, we provide a high-level classification of current privacy assurance practices. We identify three categories that are based on who is responsible for

Alaa Aref El Masri; João Pedro Sousa

2009-01-01

99

Defining occupational and consumer exposure limits for enzyme protein respiratory allergens under REACH.  

PubMed

A wide range of substances have been recognized as sensitizing, either to the skin and/or to the respiratory tract. Many of these are useful materials, so to ensure that they can be used safely it is necessary to characterize the hazards and establish appropriate exposure limits. Under new EU legislation (REACH), there is a requirement to define a derived no effect level (DNEL). Where a DNEL cannot be established, e.g. for sensitizing substances, then a derived minimal effect level (DMEL) is recommended. For the bacterial and fungal enzymes which are well recognized respiratory sensitizers and have widespread use industrially as well as in a range of consumer products, a DMEL can be established by thorough retrospective review of occupational and consumer experience. In particular, setting the validated employee medical surveillance data against exposure records generated over an extended period of time is vital in informing the occupational DMEL. This experience shows that a long established limit of 60 ng/m(3) for pure enzyme protein has been a successful starting point for the definition of occupational health limits for sensitization in the detergent industry. Application to this of adjustment factors has limited sensitization induction, avoided any meaningful risk of the elicitation of symptoms with known enzymes and provided an appropriate level of security for new enzymes whose potency has not been fully characterized. For example, in the detergent industry, this has led to general use of occupational exposure limits 3-10 times lower than the 60 ng/m(3) starting point. In contrast, consumer exposure limits vary because the types of exposure themselves cover a wide range. The highest levels shown to be safe in use, 15 ng/m(3), are associated with laundry trigger sprays, but very much lower levels (e.g. 0.01 ng/m(3)) are commonly associated with other types of safe exposure. Consumer limits typically will lie between these values and depend on the actual exposure associated with product use. PMID:20026217

Basketter, D A; Broekhuizen, C; Fieldsend, M; Kirkwood, S; Mascarenhas, R; Maurer, K; Pedersen, C; Rodriguez, C; Schiff, H-E

2009-12-21

100

Identifying an indoor air exposure limit for formaldehyde considering both irritation and cancer hazards  

PubMed Central

Formaldehyde is a well-studied chemical and effects from inhalation exposures have been extensively characterized in numerous controlled studies with human volunteers, including asthmatics and other sensitive individuals, which provide a rich database on exposure concentrations that can reliably produce the symptoms of sensory irritation. Although individuals can differ in their sensitivity to odor and eye irritation, the majority of authoritative reviews of the formaldehyde literature have concluded that an air concentration of 0.3 ppm will provide protection from eye irritation for virtually everyone. A weight of evidence-based formaldehyde exposure limit of 0.1 ppm (100 ppb) is recommended as an indoor air level for all individuals for odor detection and sensory irritation. It has recently been suggested by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (US EPA) that formaldehyde is causally associated with nasopharyngeal cancer (NPC) and leukemia. This has led US EPA to conclude that irritation is not the most sensitive toxic endpoint and that carcinogenicity should dictate how to establish exposure limits for formaldehyde. In this review, a number of lines of reasoning and substantial scientific evidence are described and discussed, which leads to a conclusion that neither point of contact nor systemic effects of any type, including NPC or leukemia, are causally associated with exposure to formaldehyde. This conclusion supports the view that the equivocal epidemiology studies that suggest otherwise are almost certainly flawed by identified or yet to be unidentified confounding variables. Thus, this assessment concludes that a formaldehyde indoor air limit of 0.1 ppm should protect even particularly susceptible individuals from both irritation effects and any potential cancer hazard.

Golden, Robert

2011-01-01

101

Determining the influence of population variation on compliance with radiofrequency exposure limits: proposed study.  

PubMed

Currently, compliance with safety limits for human exposure to radiofrequency (RF) fields is demonstrated by methods that rely on certain assumptions and approximations, which include among other things, human anatomical features, tissue types and the dielectric properties of these tissues. This paper reviews some of the available data and outlines a proposal for an encompassing study to investigate which of these assumptions are appropriate; what approximation can be used in physical and computational modeling of humans for specific energy absorption rate (SAR) calculations (a key compliance metric); and what trade-offs can be made between accuracy and modeling requirements for practical considerations. Key issues to be investigated are how SAR varies between children and adults, between males and females, and how to model SAR in the fetus of pregnant females. It is hoped that the proposed study will produce models and methods which allow for faster, more accurate and more efficient compliance with radiofrequency exposure limits. PMID:17282864

Sauren, Maia; McKenzie, Ray; Cosic, Irena

2005-01-01

102

Early limited nitrosamine exposures exacerbate high fat diet-mediated type 2 diabetes and neurodegeneration  

Microsoft Academic Search

BACKGROUND: Type 2 diabetes mellitus (T2DM) and several types of neurodegeneration, including Alzheimer's, are linked to insulin-resistance, and chronic high dietary fat intake causes T2DM with mild neurodegeneration. Intra-cerebral Streptozotocin, a nitrosamine-related compound, causes neurodegeneration, whereas peripheral treatment causes DM. HYPOTHESIS: Limited early exposures to nitrosamines that are widely present in the environment, enhance the deleterious effects of high fat

Ming Tong; Lisa Longato; Suzanne M de la Monte

2010-01-01

103

Exposure to nicotine enhances acquisition of ethanol drinking by laboratory rats in a limited access paradigm  

Microsoft Academic Search

Observations in humans suggest that the initial use of tobacco occurs in close temporal proximity to experimentation with\\u000a alcohol. There have been relatively few research reports, however, examining possible interactions between these two agents.\\u000a The present experiments examined the effect of nicotine exposure on the acquisition of ethanol drinking behavior in a limited\\u000a access procedure. In experiment 1, rats were

Brian R. Smith; Joanne T. Horan; Stephane Gaskin; Zalman Amit

1999-01-01

104

PBS performance evaluation under a high-accelerating-voltage e-beam exposure  

NASA Astrophysics Data System (ADS)

Advanced reticle fabrication, including phase-shifting mask (PSM) and optical proximity correction (OPC) reticle, has created a growing needs for a resist system with wider process latitude, superior linearity and fidelity, which lead to better CD uniformity. Some of aqueous-based DNQ-novolak resist systems, including chemical amplified one, have been proposed, however, their feasibility has not reached a practical level yet. Accordingly there seem to be many activities, in the industry at present, in re-establishing a new process technique and condition with conventional high-molecular polymer resists such as PBSTM particularly in utilizing a 'thin resist' coated blanks. Figure 1a shows e-beam resist trend of leading-edge 6' square and 250 mils thick (6025TM) photomask blanks shipment in '96 world-wide from our photomask blanks factory. High molecular polymer resist is still the major, and the top five resists have roughly 90% share, which are PBS, EBR-9TM, EBR-9 HS31TM, ZEP810TM and ZEP7000TM. Figure 1b shows 6025 PBS blanks shipment per coating thickness in '96. Thin PBS was started utilizing from '91, and had 17% share out of all 6025 PBS blanks shipment in '96. In order to reduce reticle CD error sources due to blanks, we have been doing exploratory study to determine the optimal resist process conditions in coating thickness and post-spin baking (PSB), exposure, dose as well, which enables us to appreciate real advantages of 'thin resist.' And we reported the results and its efficacy in patterning performance at Photomask Japan '97. In the report, 250 nm thick was selected particularly for PBS since it was a kind of standard as thin PBS already in the industry, while 300 nm thick was selected for the other four resists as our investigation results. Our study also resulted that only PBS had an inferiority in CD linearity as compared with the other four resists, but, exposure was done at 10 kV for PBS and 20 kV for the others. Then, we looked for an optimal PBS coating thickness again for suitable pattern resolution and risk of clear defect quality. We also tried to see an impact of e-beam accelerating voltage especially for PBS linearity and fidelity improvement this time. This paper describes our investigation results on optimum conditions in coating thickness, post-spin baking and exposure dose, as well as comparison results on patterning performance of thin resist coating between the top five conventional resists, PBS, EBR-9, EBR-9 HS31, ZEP-810 and ZEP-7000, for advanced e-beam reticle fabrication. An impact of e-beam accelerating voltage up on PBS patterning performance is also reported in this paper.

Kobayashi, Hideo; Higuchi, Takao; Asakawa, Keishi; Yokoya, Yasunori

1997-02-01

105

Fullerene c60: inhalation hazard assessment and derivation of a period-limited acceptable exposure level.  

PubMed

Fullerene C(60) has great potential for use in many industry and medical nanotechnology applications. Although the use of nanomaterials has been increasing in the recent years, limited information about its potential hazardous effects is available. Therefore, safety of nanomaterials is a world concern. Before health effects arise in workers and the general population, development and use under appropriate management are desirable. Therefore, we aimed to determine an acceptable exposure level for humans by reviewing the limited animal toxicity data available. Here, we present an initial hazard assessment, including a review of the available toxicity information of the effects of C(60) on the lungs. We then estimated the no-observed-adverse-effect level (NOAEL) of C(60) on rat lung toxicity by using lung retention of C(60) in inhalation exposure and intratracheal instillation tests. The NOAEL of C(60) on rat lung toxicity was estimated to be 3.1 mg/m(3). Because this is the NOAEL for subchronic toxicity, a period-limited acceptable exposure level (AEL(PL)) for humans was proposed, which assumed 15 years of exposure and modification within the next 10 years since more knowledge will be gained in the future. The AEL(PL) of C(60) particles with a geometric mean of 96 nm and a geometric standard deviation (GSD) of 2.0 was estimated to be 0.39 mg/m(3) for healthy workers and 1.4 × 10(-2) mg/m(3) for the general human population. The AEL(PL) of C(60) particles with different sizes was estimated to be for healthy workers and for the general human population. PMID:21856993

Shinohara, Naohide; Gamo, Masashi; Nakanishi, Junko

2011-08-19

106

Abrasion and fatigue resistance of PDMS containing multiblock polyurethanes after accelerated water exposure at elevated temperature.  

PubMed

Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers (PDMS-urethanes). Two commercially available examples, PurSil 35 (denoted as P35) and Elast-Eon E2A (denoted as E2A), were evaluated for abrasion and fatigue resistance after immersion in 85 °C buffered water for up to 80 weeks. We previously reported that water exposure in these experiments resulted in a molar mass reduction, where the kinetics of the hydrolysis reaction is supported by a straight forward Arrhenius analysis over a range of accelerated temperatures (37-85 °C). We also showed that the ultimate tensile properties of P35 and E2A were significantly compromised when the molar mass was reduced. Here, we show that the reduction in molar mass also correlated with a reduction in both the abrasion and fatigue resistance. The instantaneous wear rate of both P35 and E2A, when exposed to the reciprocating motion of an ethylene tetrafluoroethylene (ETFE) jacketed cable, increased with the inverse of the number averaged molar mass (1/Mn). Both materials showed a change in the wear surface when the number-averaged molar mass was reduced to ?16 kg/mole, where a smooth wear surface transitioned to a 'spalling-like' pattern, leaving the wear surface with ?0.3 mm cracks that propagated beyond the contact surface. The fatigue crack growth rate for P35 and E2A also increased in proportion to 1/Mn, after the molar mass was reduced below a critical value of ?30 kg/mole. Interestingly, this critical molar mass coincided with that at which the single cycle stress-strain response changed from strain hardening to strain softening. The changes in both abrasion and fatigue resistance, key predictors for long term reliability of cardiac leads, after exposure of this class of PDMS-urethanes to water suggests that these materials are susceptible to mechanical compromise in vivo. PMID:23871543

Chaffin, Kimberly A; Wilson, Charles L; Himes, Adam K; Dawson, James W; Haddad, Tarek D; Buckalew, Adam J; Miller, Jennifer P; Untereker, Darrel F; Simha, Narendra K

2013-07-18

107

Design of a real-time adaptive NURBS interpolator with axis acceleration limit  

Microsoft Academic Search

With recent advances in high-speed and high-accuracy machining, the NURBS interpolator has shown significant effect on dealing\\u000a with the free-form curves and surfaces. The existing study aims at developing the adaptive interpolator which confines the\\u000a chord error, the tangent acceleration, and jerk. However, the excessive axis acceleration is still unavoidable at the sharp\\u000a corners and will deteriorate the contour accuracy.

Jingchun Feng; Yuhao Li; Yuhan Wang; Ming Chen

2010-01-01

108

Occupational exposure limits in Europe and Asia--continued divergence or global harmonization?  

PubMed

Occupational exposure limits (OELs) are used as a risk management tool aiming at protecting against negative health effects of occupational exposure to harmful substances. The systems of OEL development have not been standardized and divergent outcomes have been reported. However some harmonization processes have been initiated, primarily in Europe. This study investigates the state of harmonization in a global context. The OEL systems of eight Asian and seventeen European organizations are analyzed with respect to similarities and differences in: (1) the system for determining OELs, (2) the selection of substances, and (3) the levels of the OELs. The majority of the investigated organizations declare themselves to have been influenced by the American Conference of Governmental Industrial Hygienists (ACGIH), and in many cases this can be empirically confirmed. The EU harmonization process is reflected in trends towards convergence within the EU. However, comparisons of Asian and European organizations provide no obvious evidence that OELs are becoming globally harmonized. PMID:21907258

Ding, Qian; Schenk, Linda; Malkiewicz, Katarzyna; Hansson, Sven Ove

2011-08-31

109

Relative Humidity in Limited Streamer Tubes for Stanford Linear Accelerator Center's BaBar Detector  

SciTech Connect

The BABAR Detector at the Stanford Linear Accelerator Center studies the decay of B mesons created in e{sup +}e{sup -} collisions. The outermost layer of the detector, used to detect muons and neutral hadrons created during this process, is being upgraded from Resistive Plate Chambers (RPCs) to Limited Streamer Tubes (LSTs). The standard-size LST tube consists of eight cells, where a silver-plated wire runs down the center of each. A large potential difference is placed between the wires and ground. Gas flows through a series of modules connected with tubing, typically four. LSTs must be carefully tested before installation, as it will be extremely difficult to repair any damage once installed in the detector. In the testing process, the count rate in most modules showed was stable and consistent with cosmic ray rate over an approximately 500 V operating range between 5400 to 5900 V. The count in some modules, however, was shown to unexpectedly spike near the operation point. In general, the modules through which the gas first flows did not show this problem, but those further along the gas chain were much more likely to do so. The suggestion was that this spike was due to higher humidity in the modules furthest from the fresh, dry inflowing gas, and that the water molecules in more humid modules were adversely affecting the modules' performance. This project studied the effect of humidity in the modules, using a small capacitive humidity sensor (Honeywell). The sensor provided a humidity-dependent output voltage, as well as a temperature measurement from a thermistor. A full-size hygrometer (Panametrics) was used for testing and calibrating the Honeywell sensors. First the relative humidity of the air was measured. For the full calibration, a special gas-mixing setup was used, where relative humidity of the LST gas mixture could be varied from almost dry to almost fully saturated. With the sensor calibrated, a set of sensors was used to measure humidity vs. time in the LSTs. The sensors were placed in two sets of LST modules, one gas line flowing through each set. These modules were tested for count rate v. voltage while simultaneously measuring relative humidity in each module. One set produced expected readings, while the other showed the spike in count rate. The relative humidity in the two sets of modules looked very similar, but it rose significantly for modules further along the gas chain.

Lang, M.I.; /MIT; Convery, M.; /SLAC; Menges, W.; /Queen Mary, U. of London

2005-12-15

110

Occupational exposure limits based on biological monitoring: the Japan Society for Occupational Health  

Microsoft Academic Search

The Japan Society for Occupational Health started to recommend an occupational exposure limit based on biological monitoring\\u000a (OEL-B) in 1993. Up to 1998, OEL-Bs for mercury, lead, hexane and 3,3?-dichloro-4,4?-diaminodiphenylmethane had been adopted\\u000a and those for 17 chemical substances (arsenic, cadmium, chromium, nickel, acetone, methanol, benzene, toluene, xylene, styrene,\\u000a tetrachloroethylene, trichloroethylene, N,N-dimethylacetoamide, N,N-dimethylformamide,carbon disulfide, carbon monoxide, and organophospate insecticides) are

K. Omae; T. Takebayashi; H. Sakurai

1999-01-01

111

Silica-associated limited systemic sclerosis after occupational exposure to calcined diatomaceous earth.  

PubMed

Silica-associated systemic sclerosis can occur in persons using calcined diatomaceous earth for filtration purpose. A limited systemic sclerosis was diagnosed in a 52-year-old male winegrower who had a combination of Raynaud's phenomenon, oesophageal dysfunction, sclerodactyly and telangectasia. The anti-centromere antibodies titre was 1/5000. The patient was frequently exposed to high atmospheric concentrations of calcined diatomaceous earth when performing the filtration of wines. Calcined diatomaceous earth is almost pure crystalline silica under the cristobalite form. The diagnosis of silica-associated limited systemic sclerosis after exposure to calcined diatomaceous earth was made. The patient's disease met the medical, administrative and occupational criteria given in the occupational diseases list 22 bis of the agriculture Social Security scheme and thence was presumed to be occupational in origin, without need to be proved. The diagnosis of occupational disease had been recognized by the compensation system of the agricultural health insurance. PMID:20605509

Moisan, Stéphanie; Rucay, Pierre; Ghali, Alaa; Penneau-Fontbonne, Dominique; Lavigne, Christian

2010-06-04

112

Pulmonary evaluation of permissible exposure limit of syntroleum S-8 synthetic jet fuel in mice.  

PubMed

No current studies have systematically examined pulmonary health effects associated with Syntroleum S-8 synthetic jet fuel (S-8). In order to gain an understanding about the threshold concentration in which lung injury is observed, C57BL/6 male mice were nose-only exposed to S-8 for 1 h/day for 7 days at average concentrations of 0 (control), 93, 352, and 616 mg/m(3). Evaluation of pulmonary function, airway epithelial barrier integrity, and pathohistology was performed 24 h after the final exposures. Significant decreases were detected in expiratory lung resistance and total lung compliance of the 352 mg/m(3) group, for which no clear concentration-dependent alterations could be determined. No significant changes in respiratory permeability were exhibited, indicating that there was no loss of epithelial barrier integrity following S-8 exposure. However, morphological examination and morphometric analysis of distal lung tissue, by using transmission electron microscopy, revealed cellular damage in alveolar type II epithelial cells, with significant increases in volume density of lamellar bodies/vacuoles at 352 and 616 S-8 mg/m(3). Moreover, terminal bronchiolar Clara injury, as evidenced by apical membrane blebs, was observed at relatively low concentrations, suggesting if this synthetic jet fuel is utilized, the current permissible exposure limit of 350 mg/m(3) for hydrocarbon fuels should cautiously be applied. PMID:19357071

Wong, Simon S; Thomas, Alana; Barbaris, Brian; Lantz, R Clark; Witten, Mark L

2009-04-07

113

Adhesion of oral Candida albicans isolates to denture acrylic following limited exposure to antifungal agents.  

PubMed

Candidal adherence to denture acrylic surfaces is implicated as the first step in the pathogenesis of Candida-associated denture stomatitis, the most prevalent form of oral candidosis in the West. This condition is treated by topically administered antifungal agents, mainly belonging to the polyenes and azoles. As the intraoral concentrations of antifungals fluctuate considerably due to the dynamics of the oral environment, the effect of short exposure to sublethal concentrations of antifungals on the adhesion of Candida albicans to denture acrylic surfaces was investigated. Seven oral C. albicans isolates were exposed to four-eight times minimum inhibitory concentrations (MIC) of five antifungal drugs, nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole, for 1 h. After removing the drug (by repeated washing) the adhesion of these isolates to acrylic strips was assessed by an in vitro adhesion assay. Exposure to antifungal agents significantly reduced the adherence of all seven C. albicans isolates to denture acrylic. The mean percentage reductions of adhesion after limited exposure to nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole were 86.48, 90.85, 66.72, 65.88 and 47.42%, respectively. These findings indicate that subtherapeutic doses of antifungals may modulate oral candidal colonization. Further, these results may have an important bearing on dosage regimens currently employed in treating oral candidosis. PMID:9877331

Ellepola, A N; Samaranayake, L P

1998-12-01

114

Pulmonary Evaluation of Permissible Exposure Limit of Syntroleum S-8 Synthetic Jet Fuel in Mice  

PubMed Central

No current studies have systematically examined pulmonary health effects associated with Syntroleum S-8 synthetic jet fuel (S-8). In order to gain an understanding about the threshold concentration in which lung injury is observed, C57BL/6 male mice were nose-only exposed to S-8 for 1 h/day for 7 days at average concentrations of 0 (control), 93, 352, and 616 mg/m3. Evaluation of pulmonary function, airway epithelial barrier integrity, and pathohistology was performed 24 h after the final exposures. Significant decreases were detected in expiratory lung resistance and total lung compliance of the 352 mg/m3 group, for which no clear concentration-dependent alterations could be determined. No significant changes in respiratory permeability were exhibited, indicating that there was no loss of epithelial barrier integrity following S-8 exposure. However, morphological examination and morphometric analysis of distal lung tissue, by using transmission electron microscopy, revealed cellular damage in alveolar type II epithelial cells, with significant increases in volume density of lamellar bodies/vacuoles at 352 and 616 S-8 mg/m3. Moreover, terminal bronchiolar Clara injury, as evidenced by apical membrane blebs, was observed at relatively low concentrations, suggesting if this synthetic jet fuel is utilized, the current permissible exposure limit of 350 mg/m3 for hydrocarbon fuels should cautiously be applied.

Wong, Simon S.; Thomas, Alana; Barbaris, Brian; Lantz, R. Clark; Witten, Mark L.

2009-01-01

115

Gut microbiota limits heavy metals burden caused by chronic oral exposure.  

PubMed

Environmental exposure to pollutants such as heavy metal(s) is responsible for various altered physiological functions which are detrimental for health. The gut microbiota is critical for intestinal homeostasis but its role on xenobiotic handling is not fully understood, especially when continuous sub-chronic exposure is addressed. We first confirmed the essential role of the intestinal microbiome to limit heavy metal body burden by using germ-free mice following 6-weeks oral exposure. Significant increases of cadmium and lead absorption and dissemination in blood and target organs were measured in germ-free mice when compared with conventional specific pathogen free (SPF) mice. Besides the "barrier" function of the luminal microbiota, this may involve specific host-genes such as metallothioneins, which are differentially expressed in the gastrointestinal tract of each group of mice. Considering genes relevant for divalent metal transporters and oxidative pathways, significant differences in basal gene expression were measured between control and germ-free mice. Moreover, the magnitude of induction of these genes upon stimulation by heavy metals varied greatly depending on the dose and type of metal as well as the microbial status of the animal. Collectively, these data illustrate the complex host-microbes interplay occurring with environmental pollutants inside the gut. PMID:23916686

Breton, Jérôme; Daniel, Catherine; Dewulf, Joëlle; Pothion, Stéphanie; Froux, Nathalie; Sauty, Mathieu; Thomas, Patrick; Pot, Bruno; Foligné, Benoît

2013-08-02

116

Minimum-Time Travel for a Vehicle with Acceleration Limits: Theoretical Analysis and Receding-Horizon Implementation  

Microsoft Academic Search

A methodology is proposed to generate minimum-time optimal velocity profiles for a vehicle with prescribed acceleration limits\\u000a along a specified path. The necessary optimality conditions are explicitly derived, allowing the construction of the optimal\\u000a solution semianalytically. A receding horizon implementation is also proposed for the on-line implementation of the velocity\\u000a optimizer. Robustness of the receding horizon algorithm is guaranteed by

Efstathios Velenis; Panagiotis Tsiotras

2008-01-01

117

Evaluation of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients  

PubMed Central

AIMS To examine the predictive performance of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients. METHODS Twenty full tacrolimus area under the concentration–time curve from 0 to 12 h post-dose (AUC0–12) profiles (AUCf) were collected from 20 subjects. Predicted tacrolimus AUC0–12 (AUCp) was calculated using the following: (i) 42 multiple regression-derived limited sampling strategies (LSSs); (ii) five population pharmacokinetic (PK) models in the Bayesian forecasting program TCIWorks; and (iii) a Web-based consultancy service. Correlations (r2) between C0 and AUCf and between AUCp and AUCf were examined. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated. RESULTS Correlation between C0 and AUCf was 0.53. Using the 42 LSS equations, correlation between AUCp and AUCf ranged from 0.54 to 0.99. The MPPE and MAPE were <15% for 29 of 42 equations (62%), including five of eight equations based on sampling taken ?2 h post-dose. Using the PK models in TCIWorks, AUCp derived from only C0 values showed poor correlation with AUCf (r2 = 0.27–0.54) and unacceptable imprecision (MAPE 17.5–31.6%). In most cases, correlation, bias and imprecision estimates progressively improved with inclusion of a greater number of concentration time points. When concentration measurements at 0, 1, 2 and 4 h post-dose were applied, correlation between AUCp and AUCf ranged from 0.75 to 0.93, and MPPE and MAPE were <15% for all models examined. Using the Web-based consultancy service, correlation between AUCp and AUCf was 0.74, and MPPE and MAPE were 6.6 and 9.6%, respectively. CONCLUSIONS Limited sampling methods better predict tacrolimus exposure compared with C0 measurement. Several LSSs based on sampling taken 2 h or less post-dose predicted exposure with acceptable bias and imprecision. Generally, Bayesian forecasting methods required inclusion of a concentration measurement from <2 h post-dose to adequately predict exposure.

Barraclough, Katherine A; Isbel, Nicole M; Kirkpatrick, Carl M; Lee, Katie J; Taylor, Paul J; Johnson, David W; Campbell, Scott B; Leary, Diana R; Staatz, Christine E

2011-01-01

118

Early limited nitrosamine exposures exacerbate high fat diet-mediated type 2 diabetes and neurodegeneration  

PubMed Central

Background Type 2 diabetes mellitus (T2DM) and several types of neurodegeneration, including Alzheimer's, are linked to insulin-resistance, and chronic high dietary fat intake causes T2DM with mild neurodegeneration. Intra-cerebral Streptozotocin, a nitrosamine-related compound, causes neurodegeneration, whereas peripheral treatment causes DM. Hypothesis Limited early exposures to nitrosamines that are widely present in the environment, enhance the deleterious effects of high fat intake in promoting T2DM and neurodegeneration. Methods Long Evans rat pups were treated with N-nitrosodiethylamine (NDEA) by i.p. injection, and upon weaning, they were fed with high fat (60%; HFD) or low fat (5%; LFD) chow for 8 weeks. Cerebella were harvested to assess gene expression, and insulin and insulin-like growth factor (IGF) deficiency and resistance in the context of neurodegeneration. Results HFD ± NDEA caused T2DM, neurodegeneration with impairments in brain insulin, insulin receptor, IGF-2 receptor, or insulin receptor substrate gene expression, and reduced expression of tau and choline acetyltransferase (ChAT), which are regulated by insulin and IGF-1. In addition, increased levels of 4-hydroxynonenal and nitrotyrosine were measured in cerebella of HFD ± NDEA treated rats, and overall, NDEA+HFD treatment reduced brain levels of Tau, phospho-GSK-3? (reflecting increased GSK-3? activity), glial fibrillary acidic protein, and ChAT to greater degrees than either treatment alone. Finally, pro-ceramide genes, examined because ceramides cause insulin resistance, oxidative stress, and neurodegeneration, were significantly up-regulated by HFD and/or NDEA exposure, but the highest levels were generally present in brains of HFD+NDEA treated rats. Conclusions Early limited exposure to nitrosamines exacerbates the adverse effects of later chronic high dietary fat intake in promoting T2DM and neurodegeneration. The mechanism involves increased generation of ceramides and probably other toxic lipids in brain.

2010-01-01

119

Effects of levels of cigarette smoke exposure on symptom-limited spiroergometry.  

PubMed

Previous investigations demonstrated reduced exposure to selected cigarette smoke constituents in adult smokers switching from conventional cigarettes (CC) to an electrically heated cigarette smoking system (EHCSS). This study investigated whether reduced exposure and no smoking (NS) would improve exercise performance. In a 3-period crossover study, 18 male adult smokers (age, 43.6+/-5.3 years) of CC were randomized to smoke CC (tar, 11 mg; nicotine, 0.8 mg; carbon monoxide, 11 mg), to use EHCSS (tar, 3 mg; nicotine, 0.2 mg; carbon monoxide, 0.4 mg [Federal Trade Commission method]), or to NS for 3 days before performing symptom-limited spiroergometry. NS and EHCSS vs CC resulted in less severe dyspnea (NS, 44.4% [P<.01 vs CC;] EHCSS, 50% [P=.03 vs CC;] CC, 88.9%), higher working capacity (NS, 2.92+/-0.4 W/kg [P=.06 vs CC;] ECHSS, 2.92+/-0.4 W/kg [P=.04 vs CC;] CC, 2.86+/-0.5 W/kg), higher peak oxygen uptake (NS, 2694+/-466 mL O(2)/min [P=.08 vs CC;] EHCSS, 2830+/-606 mL O(2)/min [P=.03 vs CC;] CC, 2682+/-492 mL O(2)/min), higher anaerobic threshold (NS, 1324+/-306 mL O(2)/min; EHCSS, 1396+/-312 mL O(2)/min [P=.03 vs CC;] CC, 1315+/-290 mL O(2)/min), and higher maximum rate-pressure product (NS, 30.1+/-2.7 x 10(3) mm Hg/min; EHCSS, 2.8 x 10(3) mm Hg/min [P<.01 vs CC;] CC, 30.7+/-29.2+/-3.6 x 10(3) mm Hg/min) indicating that reduced exposure from tobacco smoke and NS for 3 days may improve cardiovascular function as detected by symptom-limited spiroergometry. PMID:17396059

Unverdorben, Martin; der Bijl, Avan; Potgieter, Linda; Liang, Qiwei; Meyer, Bernhardt H; Roethig, Hans J

2007-01-01

120

Exposure to 56Fe-particle radiation accelerates electrophysiological alterations in the hippocampus of APP23 transgenic mice.  

PubMed

Abstract An unavoidable complication of space travel is exposure to high-charge, high-energy (HZE) particles. In animal studies, exposure of the CNS to HZE-particle radiation leads to neurological alterations similar to those seen in aging or Alzheimer's disease. In this study we examined whether HZE-particle radiation accelerated the age-related neuronal dysfunction that was previously described in transgenic mice overexpressing human amyloid precursor protein (APP). These APP23 transgenic mice exhibit age-related behavioral abnormalities and deficits in synaptic transmission. We exposed 7-week-old APP23 transgenic males to brain-only (56)Fe-particle radiation (600 MeV/nucleon; 1, 2, 4 Gy) and recorded synaptic transmission in hippocampal slices at 2, 6, 9, 14 and 18-24 months. We stimulated Schaeffer collaterals and recorded field excitatory postsynaptic potentials (fEPSP) and population spikes (PS) in CA1 neurons. Radiation accelerated the onset of age-related fEPSP decrements recorded at the PS threshold from 14 months of age to 9 months and reduced synaptic efficacy. At 9 months, radiation also reduced PS amplitudes. At 6 months, we observed a temporary deficit in paired-pulse inhibition of the PS at 2 Gy. Radiation did not significantly affect survival of APP23 transgenic mice. We conclude that irradiation of the brain with HZE particles accelerates Alzheimer's disease-related neurological deficits. PMID:20199219

Vlkolinsky, R; Titova, E; Krucker, T; Chi, B B; Staufenbiel, M; Nelson, G A; Obenaus, A

2010-03-01

121

Graphic-processing-unit-accelerated real-time exposure fusion method using pixel-level optimal exposure criterion  

NASA Astrophysics Data System (ADS)

High dynamic range (HDR) imaging is an important and challenging research topic in computational photography. A simple but effective image fusion method is proposed to accomplish the multi-exposure image composition in both static and dynamic scenes. The foundation of the proposed method is an experiential criterion that optimizes the exposure that occurs at a dramatic alteration point in the low dynamic range image sequence (LDRI). To extract these well-exposed pixel vectors, each pixel curve formed by the pixel vectors at same position along all frames in the LDRIs is first preprocessed by the chord length parameterization. Then a single high-quality pseudo-HDR image can be extracted directly and efficiently from the LDRIs using a pixel-level fusion index matrix derived from the first- and second-order difference quotients of the preprocessed pixel curves. The main advantage of the proposed method is its use of a single independent pixel in computing. It is highly parallel, allowing a graphic processing unit-based, real-time implementation. The experiments on various scenes discussed here indicate that the proposed exposure fusion method can combine a large image sequence with 10 megapixels into a visually compelling pseudo-HDR image at a rate of 30 frames/s on a consumer hardware.

Zhang, Jun; Hu, Shiqiang

2012-07-01

122

Accelerator mass spectrometry in the biomedical sciences: Applications in low-exposure biomedical and environmental dosimetry.  

National Technical Information Service (NTIS)

We are utilizing Accelerator Mass Spectrometry (AMS) as a sensitive detector for tracking the disposition of radio-isotope labeled molecules in the biomedical sciences. These applications have shown the effectiveness of AMS as a tool to quantify biologica...

J. S. Felton K. W. Turteltaub J. S. Vogel R. Balhorn B. L. Gledhill

1990-01-01

123

Multi-walled carbon nanotubes (Baytubes): approach for derivation of occupational exposure limit.  

PubMed

Carbon nanotubes come in a variety of types, but one of the most common forms is multi-walled carbon nanotubes (MWCNT). This paper focuses on the dose-response and time course of pulmonary toxicity of Baytubes, a more flexible MWCNT type with the tendency to form assemblages of nanotubes. This MWCNT has been examined in previous single and repeated exposure 13-week rat inhalation studies. Kinetic endpoints and the potential to translocate to extrapulmonary organs have been examined during postexposure periods of 3 and 6 months, respectively. The focus of both studies was to compare dosimetric endpoints and the time course of pulmonary inflammation characterized by repeated bronchoalveolar lavage and histopathology during the respective follow-up periods. To better understand the etiopathology of pulmonary inflammation and time-related lung remodeling, two metrics of retained lung dose were compared. The first used the mass metric based on the exposure concentration obtained by filter analyses and aerodynamic particle size of airborne MWCNT. The second was based on calculated volumetric lung burdens of retained MWCNT. Kinetic analyses of lung burdens support the conclusion that Baytubes, in principal, act like poorly soluble agglomerated carbonaceous particulates. However, the difference in pulmonary toxic potency (mass-based) appears to be associated with the low-density (approximately 0.1-0.3g/m(3)) of the MWCNT assemblages. Of note is that assemblages of MWCNT were found predominantly both in the exposure atmosphere and in digested alveolar macrophages. Isolated fibers were not observed in exposure atmospheres or biological specimens. All findings support the conclusion that the low specific density of microstructures was conducive to attaining the volumetric lung overload-related inflammatory response conditions earlier than conventional particles. Evidence of extrapulmonary translocation or toxicity was not found in any study. Thus, pulmonary overload is believed to trigger the cascade of events leading to a stasis of clearance and consequently increased MWCNT doses high enough to trigger sustained pulmonary inflammation. This mechanism served as conceptual basis for the calculation of the human equivalent concentration. Accordingly, multiple interspecies adjustments were necessary which included species-specific differences in alveolar deposition, differences in ventilation, and the time-dependent particle accumulation accounting for the known species-specific differences in particle clearance half-times in rats and humans. Based on this rationale and the NOAEL (no-observed adverse effect level) from the 13-week subchronic inhalation study on rats, an occupational exposure limit (OEL) of 0.05 mg Baytubes/m(3) (time weighted average) is considered to be reasonably protective to prevent lung injury to occur in the workplace environment. PMID:20074606

Pauluhn, Jürgen

2010-01-13

124

Probing the limits to muscle-powered accelerations: lessons from jumping bullfrogs.  

PubMed

The function of many muscles during natural movements is to accelerate a mass. We used a simple model containing the essential elements of this functional system to investigate which musculoskeletal features are important for increasing the mechanical work done in a muscle-powered acceleration. The muscle model consisted of a muscle-like actuator with frog hindlimb muscle properties, operating across a lever to accelerate a load. We tested this model in configurations with and without a series elastic element and with and without a variable mechanical advantage. When total muscle shortening was held constant at 30%, the model produced the most work when the muscle operated with a series elastic element and an effective mechanical advantage that increased throughout the contraction (31 J kg(-1) muscle vs 26.6 J kg(-1) muscle for the non-compliant, constant mechanical advantage configuration). We also compared the model output with the dynamics of jumping bullfrogs, measured by high-speed video analysis, and the length changes of the plantaris muscle, measured by sonomicrometry. This comparison revealed that the length, force and power trajectory of the body of jumping frogs could be accurately replicated by a model of a fully active muscle operating against an inertial load, but only if the model muscle included a series elastic element. Sonomicrometer measurements of the plantaris muscle revealed an unusual, biphasic pattern of shortening, with high muscle velocities early and late in the contraction, separated by a period of slow contraction. The model muscle produced this pattern of shortening only when an elastic element was included. These results demonstrate that an elastic element can increase the work output in a muscle-powered acceleration. Elastic elements uncouple muscle fiber shortening velocity from body movement to allow the muscle fibers to operate at slower shortening velocities and higher force outputs. A variable muscle mechanical advantage improves the effectiveness of elastic energy storage and recovery by providing an inertial catch mechanism. These results can explain the high power outputs observed in jumping frogs. More generally, our model suggests how the function of non-muscular elements of the musculoskeletal system enhances performance in muscle-powered accelerations. PMID:12819264

Roberts, Thomas J; Marsh, Richard L

2003-08-01

125

Limits of NbTi and Nb3Sn, and development of W& R Bi-2212 High Field Accelerator Magnets  

SciTech Connect

NbTi accelerator dipoles are limited to magnetic fields (H) of about 10 T, due to an intrinsic upper critical field (H{sub c2}) limitation of 14 T. To surpass this restriction, prototype Nb{sub 3}Sn magnets are being developed which have reached 16 T. We show that Nb{sub 3}Sn dipole technology is practically limited to 17 to 18 T due to insufficient high field pinning, and intrinsically to 20 to 22 T due to H{sub c2} limitations. Therefore, to obtain magnetic fields approaching 20 T and higher, a material is required with a higher H{sub c2} and sufficient high field pinning capacity. A realistic candidate for this purpose is Bi-2212, which is available in round wires and sufficient lengths for the fabrication of coils based on Rutherford-type cables. We initiated a program to develop the required technology to construct accelerator magnets from 'wind-and-react' (W&R) Bi-2212 coils. We outline the complications that arise through the use of Bi-2212, describe the development paths to address these issues, and conclude with the design of W&R Bi-2212 sub-scale magnets.

Cheng, Daniel; Dietderich, Daniel; Ferrracin, Paolo; Prestemon, Soren; Sabbi, GianLuca; Scanlan, Ron; Godeke, A.

2007-06-01

126

Experiences from occupational exposure limits set on aerosols containing allergenic proteins.  

PubMed

Occupational exposure limits (OELs) together with determined airborne exposures are used in risk assessment based managements of occupational exposures to prevent occupational diseases. In most countries, OELs have only been set for few protein-containing aerosols causing IgE-mediated allergies. They comprise aerosols of flour dust, grain dust, wood dust, natural rubber latex, and the subtilisins, which are proteolytic enzymes. These aerosols show dose-dependent effects and levels have been established, where nearly all workers may be exposed without adverse health effects, which are required for setting OELs. Our aim is to analyse prerequisites for setting OELs for the allergenic protein-containing aerosols. Opposite to the key effect of toxicological reactions, two thresholds, one for the sensitization phase and one for elicitation of IgE-mediated symptoms in sensitized individuals, are used in the OEL settings. For example, this was the case for flour dust, where OELs were based on dust levels due to linearity between flour dust and its allergen levels. The critical effects for flour and grain dust OELs were different, which indicates that conclusion by analogy (read-across) must be scientifically well founded. Except for subtilisins, no OEL have been set for other industrial enzymes, where many of which are high volume chemicals. For several of these, OELs have been proposed in the scientific literature during the last two decades. It is apparent that the scientific methodology is available for setting OELs for proteins and protein-containing aerosols where the critical effect is IgE sensitization and IgE-mediated airway diseases. PMID:22843406

Nielsen, Gunnar D; Larsen, Søren T; Hansen, Jitka S; Poulsen, Lars K

2012-07-28

127

Experiences from Occupational Exposure Limits Set on Aerosols Containing Allergenic Proteins  

PubMed Central

Occupational exposure limits (OELs) together with determined airborne exposures are used in risk assessment based managements of occupational exposures to prevent occupational diseases. In most countries, OELs have only been set for few protein-containing aerosols causing IgE-mediated allergies. They comprise aerosols of flour dust, grain dust, wood dust, natural rubber latex, and the subtilisins, which are proteolytic enzymes. These aerosols show dose-dependent effects and levels have been established, where nearly all workers may be exposed without adverse health effects, which are required for setting OELs. Our aim is to analyse prerequisites for setting OELs for the allergenic protein-containing aerosols. Opposite to the key effect of toxicological reactions, two thresholds, one for the sensitization phase and one for elicitation of IgE-mediated symptoms in sensitized individuals, are used in the OEL settings. For example, this was the case for flour dust, where OELs were based on dust levels due to linearity between flour dust and its allergen levels. The critical effects for flour and grain dust OELs were different, which indicates that conclusion by analogy (read-across) must be scientifically well founded. Except for subtilisins, no OEL have been set for other industrial enzymes, where many of which are high volume chemicals. For several of these, OELs have been proposed in the scientific literature during the last two decades. It is apparent that the scientific methodology is available for setting OELs for proteins and protein-containing aerosols where the critical effect is IgE sensitization and IgE-mediated airway diseases.

Nielsen, Gunnar D.

2012-01-01

128

Airborne asbestos concentration from brake changing does not exceed permissible exposure limit.  

PubMed

The use in the past, and to a lesser extent today, of chrysotile asbestos in automobile brake systems causes health concerns among professional mechanics. Therefore, we conducted four separate tests in order to evaluate an auto mechanic's exposure to airborne asbestos fibers while performing routine brake maintenance. Four nearly identical automobiles from 1960s having four wheel drum brakes were used. Each automobile was fitted with new replacement asbestos-containing brake shoes and then driven over a predetermined public road course for about 2253 km. Then, each car was separately brought into a repair facility; the brakes removed and replaced with new asbestos-containing shoes. The test conditions, methods, and tools were as commonly used during the 1960s. The mechanic was experienced in brake maintenance, having worked in the automobile repair profession beginning in the 1960s. Effects of three independent variables, e.g., filing, sanding, and arc grinding of the replacement brake shoe elements, were tested. Personal and area air samples were collected and analyzed for the presence of fibers, asbestos fibers, total dust, and respirable dust. The results indicated a presence in the air of only chrysotile asbestos and an absence of other types of asbestos. Airborne chrysotile fiber exposures for each test remained below currently applicable limit of 0.1 fiber/ml (eight-hour time-weighted average). PMID:12878055

Blake, Charles L; Van Orden, Drew R; Banasik, Marek; Harbison, Raymond D

2003-08-01

129

Quantitative property–property relationships for computing Occupational Exposure Limits and Vapour Hazard Ratios of organic solvents  

Microsoft Academic Search

Vapour Hazard Ratio (VHR) is used in solvent substitution to select the best replacement option regarding overexposure potential of solvents. However, VHR calculations are limited by the availability of Occupational Exposure Limits (OELs). The overall objective of this study was to develop quantitative property–property relationship (QPPR) approaches for computing OELs, in view of supporting the derivation of VHRs for solvents

M. Debia; K. Krishnan

2010-01-01

130

UVB Exposure Does Not Accelerate Rates of Litter Decomposition in a Semiarid Riparian Ecosystem  

Microsoft Academic Search

Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix-invaded riparian ecosystem during the establishment of an insect biological control agent

S. M. Uselman; K. A. Snyder; R. R. Blank; T. J. Jones

2010-01-01

131

UVB exposure does not accelerate rates of litter decomposition in a semi-arid riparian ecosystem  

Microsoft Academic Search

Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix-invaded riparian ecosystem during the establishment of an insect biological control agent

Shauna M. Uselman; Keirith A. Snyder; Robert R. Blank; Timothy J. Jones

2011-01-01

132

The NREL Outdoor Accelerated-Weathering Tracking System Photovoltaic Module Exposure Results  

SciTech Connect

Status results are presented for the Outdoor Accelerated-Weathering Tracking System (OATS) first study on photovoltaic (PV) modules. Studies began in November 1997 on pairs of commercially available crystalline silicon and amorphous silicon (a-Si) PV modules kept at constant resistive load.

Basso, T. S.

2000-01-01

133

Lack of blood formate accumulation in humans following exposure to methanol vapor at the current permissible exposure limit of 200 ppm  

SciTech Connect

Accumulation of formate, the putative toxic metabolite of methanol, in the blood and the relationship between pulmonary intake and blood methanol concentration were investigated in six human volunteers following a 6-hr exposure to 200 ppm methanol (the current Occupational Safety and Health Administration 8-hr time-weighted average permissible exposure limit). At the end of a 6-hr exposure to 200 ppm methanol at rest, the blood methanol concentration was increased from a mean of 1.8 micrograms/mL to 7.0 micrograms/mL. Under light exercise, the total amount of methanol inhaled during the 6-hr exposure period was 1.8 times that inhaled at rest. However, no statistically significant increase in blood methanol concentration was observed under exercise: the concentrations averaged 8.1 micrograms/mL. Formate did not accumulate in the blood above its background level following the 6-hr exposures to 200 ppm methanol whether subjects were exposed at rest or during exercise. Unlike the data collected from epidemiologic studies, the authors' results were obtained under well-controlled methanol exposure conditions and by using appropriate dietary restrictions. The data show that (1) the biological load of methanol would be the same regardless of whether workers are engaged in light physical activity when they are exposed to methanol vapors below 200 ppm and (2) the formate that is associated with acute methanol toxicities in humans does not accumulate in blood when methanol exposure concentrations are below 200 ppm.

Lee, E.W.; Terzo, T.S.; D'Arcy, J.B.; Gross, K.B.; Schreck, R.M. (Biomedical Science Department, General Motors Research Laboratories, Warren, MI (United States))

1992-02-01

134

Exposure limit values for nanomaterials--capacity and willingness of users to apply a precautionary approach.  

PubMed

In the European Union, the legal obligation for employers to provide a safe workplace for processing manufactured nanomaterials is a challenge when there is a lack of hazard information. The attitude of key stakeholders in industry, trade unions, branch and employers' organizations, and government policy advisors toward nano reference values (NRVs) has been investigated in a pilot study that was initiated by a coalition of Dutch employers' organizations and Dutch trade unions. NRVs are developed as provisional substitutes for health-based occupational exposure limits or derived no-effect levels and are based on a precautionary approach. NRVs have been introduced as a voluntary risk management instrument for airborne nanomaterials at the workplace. A measurement strategy to deal with simultaneously emitting process-generated nanoparticles was developed, allowing employers to use the NRVs for risk assessment. The motivational posture of most companies involved in the pilot study appears to be pro-active regarding worker protection and acquiescent to NRVs. An important driver to use NRVs seems to be a temporary certainty employers experience with regard to their legal obligation to take preventive action. Many interviewees welcome the voluntary character of NRVs, though trade unions and a few companies advocate a more binding status. PMID:23216200

van Broekhuizen, Pieter; Dorbeck-Jung, Bärbel

2013-01-01

135

Accelerated habit formation following amphetamine exposure is reversed by D1, but enhanced by D2, receptor antagonists  

PubMed Central

Repeated exposure to the psychostimulant amphetamine has been shown to disrupt goal-directed instrumental actions and promote the early and abnormal development of goal-insensitive habitual responding (Nelson and Killcross, 2006). To investigate the neuropharmacological specificity of this effect as well as restore goal-directed responding in animals with pre-training amphetamine exposure, animals were treated with the non-selective dopamine antagonist ?-flupenthixol, the selective D1 antagonist SCH 23390 or the selective D2 antagonist eticlopride, prior to instrumental training (three sessions). Subsequently, the reinforcer was paired with LiCL-induced gastric-malaise and animals were given a test of goal-sensitivity both in extinction and reacquisition. The effect of these dopaminergic antagonists on the sensitivity of lever press performance to outcome devaluation was assessed in animals with pre-training exposure to amphetamine (Experiments 1A–C) or in non-sensitized animals (Experiment 2). Both ?-flupenthixol and SCH23390 reversed accelerated habit formation following amphetamine sensitization. However, eticlopride appeared to enhance this effect and render instrumental performance compulsive as these animals were unable to inhibit responding both in extinction and reacquisition, even though a consumption test confirmed they had acquired an aversion to the reinforcer. These findings demonstrate that amphetamine induced-disruption of goal-directed behavior is mediated by activity at distinct dopamine receptor subtypes and may represent a putative model of the neurochemical processes involved in the loss of voluntary control over behavior.

Nelson, Andrew J. D.; Killcross, Simon

2013-01-01

136

UVB Exposure Does Not Accelerate Rates of Litter Decomposition in a Semiarid Riparian Ecosystem  

NASA Astrophysics Data System (ADS)

Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix-invaded riparian ecosystem during the establishment of an insect biological control agent in northern Nevada. Feeding by the northern tamarisk beetle (Diorhabda carinulata) on Tamarix spp. trees leads to altered leaf litter quality and increased exposure to solar UVB radiation from canopy opening. In addition, we examined the dynamics of litter decomposition of the invasive exotic Lepidium latifolium, because it is well-situated to invade beetle-infested Tamarix sites. Three leaf litter types (natural Tamarix, beetle-affected Tamarix, and L. latifolium) differing in substrate quality were decomposed in litterbags for one year in the field. Litterbags were subjected to one of three treatments: (1) Ambient UVB or (2) Reduced UVB (where UVB was manipulated by using clear plastic films that transmit or block UVB), and (3) No Cover (a control used to test for the effect of using the plastic films, i.e. a cover effect). Results showed a large cover effect on rates of decomposition and nutrient release, and our findings suggested that frequent cycles of freeze-thaw, and possibly rainfall intensity, influenced decomposition at this site. Contrary to our expectations, greater UVB exposure did not result in faster rates of decomposition. Greater UVB exposure resulted in decreased rates of decomposition and P release for the lower quality litter and no change in rates of decomposition and nutrient release for the two higher quality litter types, possibly due to a negative effect of UVB on soil microbes. Among litter types, rates of decomposition and net release of N and P followed this ranking: L. latifolium > beetle-affected Tamarix > natural Tamarix. Altered nutrient dynamics with beetle introduction as well as the rapid decomposition rates exhibited by L. latifolium are consistent with vulnerability to secondary invasion. In this desert ecosystem, decomposition and nutrient release were strongly affected by litter type and much less so by UVB exposure.

Uselman, S. M.; Snyder, K. A.; Blank, R. R.; Jones, T. J.

2010-12-01

137

Exposure to estradiol before but not during acquisition of LiCl-induced conditioned taste avoidance accelerates extinction.  

PubMed

Estradiol accelerates extinction of LiCl-induced conditioned taste avoidance when it is present continuously before and during acquisition. We have suggested that the effect of estradiol on extinction is due to its illness-associated, rather than learning-associated, properties. If this were the case, then one would expect estradiol to act before but not during acquisition. This expectation is based on previous work showing attenuation of learned taste avoidance when rats are given distal preexposure (greater than 24 h before conditioning) or proximal preexposure (less than 24 h before conditioning) to the illness-inducing agent LiCl before acquisition of a LiCl-induced conditioned taste avoidance. In three separate experiments, estradiol was administered during three different time periods via subcutaneous implantation of a 10-mm estradiol-filled capsule. In each experiment, the extinction of estradiol-treated females was compared to that of females implanted with empty capsules. In the first experiment, female rats were given distal exposure to estradiol before acquisition. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition. In the second experiment, female rats were given proximal exposure to estradiol before acquisition. Capsules were implanted 2.5 h before LiCl was paired with a sucrose solution and were removed 16.5 h later. In the third experiment, female rats were given exposure to estradiol during acquisition. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. The only estradiol-treated females to show accelerated extinction were those given distal preexposure to estradiol in Experiment 1. These data do not support a learning-associated hypothesis and only partially support an illness-associated hypothesis. The failure to find accelerated extinction following proximal preexposure may reflect an inappropriate choice of the parameters used in the experiment or a difference in the stimulus properties of LiCl and estradiol that allow each to serve as conditioning and preexposure agents in conditioned taste avoidance paradigms [corrected]. PMID:11971663

Chambers, Kathleen C; Hayes, Unja L

2002-05-01

138

Limits  

NSDL National Science Digital Library

Students will see how the idea of a limit can be presented both in formal epsilon-delta-style terms, and using corresponding animations. After calculating a limit for a simple example function, we point out that limits do not always exist.

Liao, David

139

LimitedKnowledgeandUseofHIVPost-andPre-Exposure Prophylaxis Among Gay and Bisexual Men  

Microsoft Academic Search

Background: Post-exposure prophylaxis (PEP) is currently recommended after certain high-risk exposures, and pre-exposure prophylaxis (PrEP) is undergoing evaluation in clinical trials. Media reports have suggested substantial levels of community PrEP use despite its unproven effectiveness. Methods: We conducted a cross-sectional survey of 1819 HIV- uninfected gay\\/bisexual men in California to assess PEP and PrEP awareness and use. Results: Overall, 47%

Albert Y. Liu; Pravina V. Kittredge; Eric Vittinghoff; H. Fisher Raymond; Katherine Ahrens; Tim Matheson; Jennifer Hecht; Jeffrey D. Klausner; Susan P. Buchbinder

2008-01-01

140

The Role of Home Smoking Bans in Limiting Exposure to Secondhand Tobacco Smoke in Hungary  

ERIC Educational Resources Information Center

|Our objective was to assess how exposure to secondhand tobacco smoke occurs in Hungarian homes, particularly among non-smokers, and to examine the effectiveness of home smoking bans in eliminating exposure to secondhand smoke at home. In 2009, 2286 non-smokers and smokers aged 16-70 years, who were selected randomly from a nationally…

Paulik, Edit; Maroti-Nagy, A.; Nagymajtenyi, L.; Rogers, T.; Easterling, D.

2013-01-01

141

The limits of predictability of volcanic eruptions from accelerating rates of earthquakes  

NASA Astrophysics Data System (ADS)

Volcanic eruptions are commonly preceded by increased rates of earthquakes. Previous studies argue that in some instances these sequences follow the inverse Omori law (IOL) and that this model could be the basis for forecasting the timing of eruption onset. However, the catalogue of pre-eruptive sequences is small, and the performance of the IOL as a forecasting tool remains largely untested. Here, we use simulations to quantify upper limits to the accuracy and bias of forecast eruption times based on the IOL in the `best-case' scenario that uncertainty only arises from model parameter estimation from single realizations of a stochastic point process. We compare different methods for forecasting based on the IOL, and demonstrate that a maximum-likelihood method yields more accurate and less-biased forecasts than methods currently employed. Even in these idealized conditions, we find that large forecast uncertainty and false alarms are inherent features of the mathematics of the IOL. For example model parameter values and 500-d pre-eruptive sequence durations, at 25 d before the eruption, 10 per cent of the forecasts are more than 8 d early or late if the power-law exponent is known a priori, and more than 18 d early or late if the power-law exponent is unknown. We also evaluate methods for model comparison and estimation of the power-law exponent. These techniques are applied to examples of real pre-eruptive earthquake data sets. We find evidence for systematic deviations from the idealized model, indicating the action of multiple processes and resulting in greater forecast error than in the synthetic examples, especially close to the eruption time.

Bell, Andrew F.; Naylor, Mark; Main, Ian G.

2013-09-01

142

Limited infection upon human exposure to a recombinant raccoon pox vaccine vector.  

PubMed

A laboratory accident resulted in human exposure to a recombinant raccoon poxvirus (RCN) developed as a vaccine vector for antigens of Yersinia pestis for protection of wild rodents (and other animals) against plague. Within 9 days, the patient developed a small blister that healed within 4 weeks. Raccoon poxvirus was cultured from the lesion, and the patient developed antibody to plague antigen (F1) and RCN. This is the first documented case of human exposure to RCN. PMID:15246608

Rocke, Tonie E; Dein, F Joshua; Fuchsberger, Martina; Fox, Barry C; Stinchcomb, Dan T; Osorio, Jorge E

2004-07-29

143

Limitations of Interview-Based Risk Assessment of RF Exposure from Appliances  

Microsoft Academic Search

This study was conducted to assess the quality of interview-based exposure estimates obtained in a large epidemiologic case-control study: The Northern Germany Leukemia and Lymphoma Study (1997-2002) (NLL). The NLL used standardized, face-to-face, computer-assisted interviews to record subjects' lifetime use of radiofrequency (RF)-emitting appliances such as cellular telephones, cordless telephones, baby monitors, and television headphones. Exposure assessment comprised 3 levels

Thomas Behrens; Claudia Terschüren; Wolfgang Hoffmann

2003-01-01

144

Mathematical modeling of acceleration in a racetrack microtron at 50 MeV with a limited number of orbits  

Microsoft Academic Search

A mathematical model of a racetrack microtron at 50 MeV is described. A special feature of the accelerator is that the transverse\\u000a dimensions of the accelerating section of the microtron are substantial. To bypass this section in the first revolution, the\\u000a acceleration factor is increased to four. Another feature of the accelerator is that the beam is injected directly into

A. M. Gromov; A. A. Vasil’ev; G. V. Solodukhov

2008-01-01

145

Association of years of occupational quartz exposure with spirometric airflow limitation in Norwegian men aged 30-46 years  

PubMed Central

BACKGROUND—The association between occupational quartz exposure and ventilatory function was investigated in men in a general population after adjusting for other potential determinants of outcome.?METHODS—All eligible men aged 30-46 years living in western Norway (n = 45 380) were invited to a cross sectional community survey. This included a self administered questionnaire (with respiratory symptoms, smoking habits and occupational exposures), spirometric recordings (using dry wedge bellow spirometers), and a chest radiograph (65% attendance). Measurements of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were obtained in 91% (n = 26 803) of those who participated, 26 106 of whom performed successful spirometric tests and had normal chest radiographs and remained for further analysis. Age, body mass index, and technician standardised residuals ((observed minus predicted value)/residual standard error) of maximum FEV1/height2 and FVC/height2 were used as outcome variables for adjusted lung function levels, respectively.?RESULTS—Occupational quartz exposure was reported by 13% (n = 3445) of those who participated in the survey, with a mean duration of seven years. Among those exposed to quartz, significant inverse linear relationships were observed between years of exposure and FEV1 level and the ratio of FEV1/FVC, independent of host characteristics. Multiple linear regression analyses showed that the difference in FEV1 associated with each year of quartz exposure was -4.3 ml (95% Cl -1.1 to -7.5 ml; p = 0.01) compared with -6.9 ml (95% Cl -4.7 to -9.1 ml; p<0.01) from smoking 20 cigarettes/day for one year after adjusting for age, atopy, asthma, wheezing, marital status, and other occupational exposures.?CONCLUSION—In men aged 30-46 years with occupational quartz exposure and normal chest radiographs the duration of occupational quartz exposure was an independent predictor for spirometric airflow limitation.??

Humerfelt, S.; Eide, G.; Gulsvik, A.

1998-01-01

146

Prenatal Arsenic Exposure Alters Gene Expression in the Adult Liver to a Proinflammatory State Contributing to Accelerated Atherosclerosis  

PubMed Central

The mechanisms by which environmental toxicants alter developmental processes predisposing individuals to adult onset chronic disease are not well-understood. Transplacental arsenic exposure promotes atherogenesis in apolipoprotein E-knockout (ApoE?/?) mice. Because the liver plays a central role in atherosclerosis, diabetes and metabolic syndrome, we hypothesized that accelerated atherosclerosis may be linked to altered hepatic development. This hypothesis was tested in ApoE?/? mice exposed to 49 ppm arsenic in utero from gestational day (GD) 8 to term. GD18 hepatic arsenic was 1.2 µg/g in dams and 350 ng/g in fetuses. The hepatic transcriptome was evaluated by microarray analysis to assess mRNA and microRNA abundance in control and exposed pups at postnatal day (PND) 1 and PND70. Arsenic exposure altered postnatal developmental trajectory of mRNA and microRNA profiles. We identified an arsenic exposure related 51-gene signature at PND1 and PND70 with several hubs of interaction (Hspa8, IgM and Hnf4a). Gene ontology (GO) annotation analyses indicated that pathways for gluconeogenesis and glycolysis were suppressed in exposed pups at PND1, and pathways for protein export, ribosome, antigen processing and presentation, and complement and coagulation cascades were induced by PND70. Promoter analysis of differentially-expressed transcripts identified enriched transcription factor binding sites and clustering to common regulatory sites. SREBP1 binding sites were identified in about 16% of PND70 differentially-expressed genes. Western blot analysis confirmed changes in the liver at PND70 that included increases of heat shock protein 70 (Hspa8) and active SREBP1. Plasma AST and ALT levels were increased at PND70. These results suggest that transplacental arsenic exposure alters developmental programming in fetal liver, leading to an enduring stress and proinflammatory response postnatally that may contribute to early onset of atherosclerosis. Genes containing SREBP1 binding sites also suggest pathways for diabetes mellitus and rheumatoid arthritis, both diseases that contribute to increased cardiovascular disease in humans.

States, J. Christopher; Singh, Amar V.; Knudsen, Thomas B.; Rouchka, Eric C.; Ngalame, Ntube O.; Arteel, Gavin E.; Piao, Yulan; Ko, Minoru S. H.

2012-01-01

147

Screening values for Non-Carcinogenic Hanford Waste Tank Vapor Chemicals that Lack Established Occupational Exposure Limits  

SciTech Connect

Over 1,500 different volatile chemicals have been reported in the headspaces of tanks used to store high-level radioactive waste at the U.S. Department of Energy's Hanford Site. Concern about potential exposure of tank farm workers to these chemicals has prompted efforts to evaluate their toxicity, identify chemicals that pose the greatest risk, and incorporate that information into the tank farms industrial hygiene worker protection program. Established occupation exposure limits for individual chemicals and petroleum hydrocarbon mixtures have been used elsewhere to evaluate about 900 of the chemicals. In this report headspace concentration screening values were established for the remaining 600 chemicals using available industrial hygiene and toxicological data. Screening values were intended to be more than an order of magnitude below concentrations that may cause adverse health effects in workers, assuming a 40-hour/week occupational exposure. Screening values were compared to the maximum reported headspace concentrations.

Poet, Torka S.; Mast, Terryl J.; Huckaby, James L.

2006-02-06

148

A practical method for compliance testing of base stations for mobile communications with exposure limits  

Microsoft Academic Search

A measurement procedure is explained which makes the combination of simple simulations, broadband and frequency-selective electromagnetic measurements to check in a practical way if a base station site complies with restrictions regarding the exposure to electromagnetic radiation. The measuring method enables the accurate and objective control of a base station site in a practical and reliable way. The procedure provides

C. Olivier; L. Martens

2001-01-01

149

Proposed Occupational Exposure Limits for Select Ethylene Glycol Ethers Using PBPK Models and Monte Carlo Simulations  

Microsoft Academic Search

Methoxyethanol (ethylene glycol monomethyl ether, EGME), ethoxyethanol (ethylene glycol monoethyl ether, EGEE), and ethoxyethyl acetate (ethylene glycol monoethyl ether acetate, EGEEA) are all developmental toxicants in laboratory animals. Due to the imprecise nature of the exposure data in epidemiology studies of these chemicals, we relied on human and animal phar- macokinetic data, as well as animal toxicity data, to derive

L. M. Sweeney; J. F. Holson; M. D. Whorton; K. M. Thompson; M. L. Gargas

150

Airborne asbestos concentration from brake changing does not exceed permissible exposure limit  

Microsoft Academic Search

The use in the past, and to a lesser extent today, of chrysotile asbestos in automobile brake systems causes health concerns among professional mechanics. Therefore, we conducted four separate tests in order to evaluate an auto mechanic’s exposure to airborne asbestos fibers while performing routine brake maintenance. Four nearly identical automobiles from 1960s having four wheel drum brakes were used.

Charles L. Blake; Drew R. Van Orden; Marek Banasik; Raymond D. Harbison

2003-01-01

151

Intratracheal Instillation as an Exposure Technique for the Evaluation of Respiratory Tract Toxicity: Uses and Limitations  

Microsoft Academic Search

The evaluation of respiratory tract toxicity from airborne materials frequently involves exposure of animals via inhalation. This provides a natural route of entry into the host and, as such, is the preferred method for the introduction of toxicants into the lungs. However, for various reasons, this technique cannot always be used, and the direct instillation of a test material into

Kevin E. Driscoll; Daniel L. Costa; Gary Hatch; Rogene Henderson; Gunter Oberdorster; Harry Salem; Richard B. Schlesingeri

2000-01-01

152

Limitations of interview-based risk assessment of RF exposure from appliances.  

PubMed

This study was conducted to assess the quality of interview-based exposure estimates obtained in a large epidemiologic case-control study: The Northern Germany Leukemia and Lymphoma Study (1997-2002) (NLL). The NLL used standardized, face-to-face, computer-assisted interviews to record subjects' lifetime use of radiofrequency (RF)-emitting appliances such as cellular telephones, cordless telephones, baby monitors, and television headphones. Exposure assessment comprised 3 levels of precision: ever use, gross vs. net appliance-years, and lifetime cumulative exposure hours. In the current study, the authors analyzed data from 3041 interviews of NLL controls, representing an age-stratified random sample of the general populations of 6 counties in Northern Germany. Weighted kappa coefficients for gross vs. net appliance-years for men were 0.59 (95% confidence interval [CI] = 0.46, 0.71) for baby monitors and 0.98 (95% CI = 0.97, 0.99) for cordless phones; for women, the coefficients were 0.68 (95% CI = 0.56, 0.79) and 0.97 (95% CI = 0.94, 0.98), respectively. Weighted kappa values were considerably lower when net appliance-years and lifetime cumulative exposure hours were compared. Study results demonstrated that interview information on use of RF-emitting appliances, when measured at different levels of precision, can result in misclassification and biased risk estimates. PMID:16238163

Behrens, Thomas; Terschüren, Claudia; Hoffmann, Wolfgang

2004-06-01

153

Learning foreign labels from a foreign speaker: the role of (limited) exposure to a second language.  

PubMed

Three- and four-year-olds (N = 144) were introduced to novel labels by an English speaker and a foreign speaker (of Nordish, a made-up language), and were asked to endorse one of the speaker's labels. Monolingual English-speaking children were compared to bilingual children and English-speaking children who were regularly exposed to a language other than English. All children tended to endorse the English speaker's labels when asked 'What do you call this?', but when asked 'What do you call this in Nordish?', children with exposure to a second language were more likely to endorse the foreign label than monolingual and bilingual children. The findings suggest that, at this age, exposure to, but not necessarily immersion in, more than one language may promote the ability to learn foreign words from a foreign speaker. PMID:22217207

Akhtar, Nameera; Menjivar, Jennifer; Hoicka, Elena; Sabbagh, Mark A

2012-01-05

154

Infant Outcomes After Maternal Antiretroviral Exposure in Resource-Limited Settings  

PubMed Central

BACKGROUND AND OBJECTIVE: The impact of maternal antiretrovirals (ARVs) during pregnancy, labor, and postpartum on infant outcomes is unclear. METHODS: Infants born to HIV-infected mothers in ARV studies were followed for 18 months. RESULTS: Between June 2006 and December 2008, 236 infants enrolled from Africa (n = 36), India (n = 47), Thailand (n = 152), and Brazil (n = 1). Exposure to ARVs in pregnancy included ?3 ARVs (10%), zidovudine/intrapartum ARV (81%), and intrapartum ARV (9%). There were 4 infant infections (1 in utero, 3 late postpartum) and 4 deaths with 1.8% mortality (95% confidence interval [CI], 0.1%–3.5%) and 96.4% HIV-1–free survival (95% CI, 94.0%–98.9%). Birth weight was ?2.5 kg in 86%. In the first 6 months, Indian infants (nonbreastfed) had lowest median weights and lengths and smallest increases in growth. After 6 months, African infants had the lowest median weight and weight-for-age z scores. Infants exposed to highest maternal viral load had the lowest height and height-for-age z scores. Serious adverse events occurred in 38% of infants, did not differ by country, and correlated with less maternal ARV exposure. Clinical diagnoses were seen in 84% of Thai, 31% of African, and 9% of Indian infants. Congenital defects/inborn errors of metabolism were seen in 18 (7.6%) infants, of which 17 were Thai (11%: 95% CI, 6.7%–17.0%); none had first trimester ARV exposure. CONCLUSIONS: Infant follow-up in large international cohorts is feasible and provides important safety and HIV transmission data following maternal ARV exposure. Increased surveillance increases identification of congenital/inborn errors.

Komarow, Lauren; Cu-Uvin, Susan; Jourdain, Gonzague; Klingman, Karin L.; Shapiro, David E.; Mofenson, Lynne; Moran, Laura; Campbell, Thomas B.; Hitti, Jane; Fiscus, Susan; Currier, Judith

2012-01-01

155

Multi-walled carbon nanotubes (Baytubes®): Approach for derivation of occupational exposure limit  

Microsoft Academic Search

Carbon nanotubes come in a variety of types, but one of the most common forms is multi-walled carbon nanotubes (MWCNT). This paper focuses on the dose–response and time course of pulmonary toxicity of Baytubes®, a more flexible MWCNT type with the tendency to form assemblages of nanotubes. This MWCNT has been examined in previous single and repeated exposure 13-week rat

Jürgen Pauluhn

2010-01-01

156

Health-based recommended occupational exposure limit for methyl ethyl ketone  

Microsoft Academic Search

The NAEL of 7500 mg MEK\\/m3 (rat, 90 days) will be taken as a starting point. In view of the absence of long-term data and carcinogenicity data a safety factor of 10 is taken. Therefore, a OEL of 7500 : 10 mg\\/m3 = 750 mg MEK\\/m3 TWA 8 hr (250 ppm) is advised for exposure to MEK alone. Since skin

M. A. Maclaine Pont

1991-01-01

157

Limitations of current dosimetry for intracavitary accelerated partial breast irradiation with high dose rate iridium-192 and electronic brachytherapy sources  

NASA Astrophysics Data System (ADS)

Intracavitary accelerated partial breast irradiation (APBI) is a method of treating early stage breast cancer using a high dose rate (HDR) brachytherapy source positioned within the lumpectomy cavity. An expandable applicator stretches the surrounding tissue into a roughly spherical or elliptical shape and the dose is prescribed to 1 cm beyond the edge of the cavity. Currently, dosimetry for these treatments is most often performed using the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism. The TG-43 dose-rate equation determines the dose delivered to a homogeneous water medium by scaling the measured source strength with standardized parameters that describe the radial and angular features of the dose distribution. Since TG-43 parameters for each source model are measured or calculated in a homogeneous water medium, the dosimetric effects of the patient's dimensions and composition are not accounted for. Therefore, the accuracy of TG-43 calculations for intracavitary APBI is limited by the presence of inhomogeneities in and around the target volume. Specifically, the breast is smaller than the phantoms used to determine TG-43 parameters and is surrounded by air, ribs, and lung tissue. Also, the composition of the breast tissue itself can affect the dose distribution. This dissertation is focused on investigating the limitations of TG-43 dosimetry for intracavitary APBI for two HDR brachytherapy sources: the VariSource TM VS2000 192Ir source and the AxxentRTM miniature x-ray source. The dose for various conditions was determined using thermoluminescent dosimeters (TLDs) and Monte Carlo (MC) calculations. Accurate measurements and calculations were achieved through the implementation of new measurement and simulation techniques and a novel breast phantom was developed to enable anthropomorphic phantom measurements. Measured and calculated doses for phantom and patient geometries were compared with TG-43 calculated doses to illustrate the limitations of TG-43 dosimetry for intracavitary APBI. TG-43 dose calculations overestimate the dose for regions approaching the lung and breast surface and underestimate the dose for regions in and beyond less-attenuating media such as lung tissue, and for lower energies, breast tissue as well.

Raffi, Julie A.

158

Cell surface hydrophobicity of oral Candida dubliniensis isolates following limited exposure to sub-therapeutic concentrations of chlorhexidine gluconate.  

PubMed

Candidal adhesion has been implicated as the initial step in the pathogenesis of oral candidiasis and cell surface hydrophobicity (CSH) has been implicated in adhesion to mucosal surfaces. Candida dubliniensis is an opportunistic pathogen associated with recurrent oral candidiasis. Chlorhexidine gluconate is by far the commonest antiseptic mouth wash prescribed in dentistry. At dosage intervals the intraoral concentration of this antiseptic fluctuates considerably and reaches sub-therapeutic levels due to the dynamics of the oral cavity. Hence, the organisms undergo only a limited exposure to the antiseptic during treatment. The impact of this antiseptic following such exposure on CSH of C. dubliniensis isolates has not been investigated. Hence, the main objective of this study was to investigate the effect of brief exposure to sub-therapeutic concentrations of chlorhexidine gluconate on the CSH of C. dubliniensis isolates. Twelve oral isolates of C. dubliniensis were briefly exposed to three sub-therapeutic concentrations of 0.005%, 0.0025% and 0.00125% chlorhexidine gluconate for 30 min. Following subsequent removal of the drug, the CSH of the isolates was determined by a biphasic aqueous-hydrocarbon assay. Compared with the controls, exposure to 0.005% and 0.0025% chlorhexidine gluconate suppressed the relative CSH of the total sample tested by 44.49% (P < 0.001) and 21.82% (P < 0.018), respectively, with all isolates being significantly affected. Although exposure to 0.00125% of chlorhexidine gluconate did not elicit a significant suppression on the total sample tested (7.01%; P > 0.05), four isolates of the group were significantly affected. These findings imply that exposure to sub-therapeutic concentrations of chlorhexidine gluconate may suppress CSH of C. dublinienis isolates, thereby reducing its pathogenicity and highlights further the pharmacodynamics of chlorhexidine gluconate. PMID:22533484

Ellepola, Arjuna N B; Joseph, Bobby K; Khan, Z U

2012-04-26

159

Analysis of human brain exposure to low-frequency magnetic fields: a numerical assessment of spatially averaged electric fields and exposure limits.  

PubMed

Compliance with the established exposure limits for the electric field (E-field) induced in the human brain due to low-frequency magnetic field (B-field) induction is demonstrated by numerical dosimetry. The objective of this study is to investigate the dependency of dosimetric compliance assessments on the applied methodology and segmentations. The dependency of the discretization uncertainty (i.e., staircasing and field singularity) on the spatially averaged peak E-field values is first determined using canonical and anatomical models. Because spatial averaging with a grid size of 0.5?mm or smaller sufficiently reduces the impact of artifacts regardless of tissue size, it is a superior approach to other proposed methods such as the 99th percentile or smearing of conductivity contrast. Through a canonical model, it is demonstrated that under the same uniform B-field exposure condition, the peak spatially averaged E-fields in a heterogeneous model can be significantly underestimated by a homogeneous model. The frequency scaling technique is found to introduce substantial error if the relative change in tissue conductivity is significant in the investigated frequency range. Lastly, the peak induced E-fields in the brain tissues of five high-resolution anatomically realistic models exposed to a uniform B-field at ICNIRP and IEEE reference levels in the frequency range of 10?Hz to 100?kHz show that the reference levels are not always compliant with the basic restrictions. Based on the results of this study, a revision is recommended for the guidelines/standards to achieve technically sound exposure limits that can be applied without ambiguity. PMID:23404214

Chen, Xi-Lin; Benkler, Stefan; Chavannes, Nicholas; De Santis, Valerio; Bakker, Jurriaan; van Rhoon, Gerard; Mosig, Juan; Kuster, Niels

2013-02-12

160

Exposure limits: the underestimation of absorbed cell phone radiation, especially in children.  

PubMed

The existing cell phone certification process uses a plastic model of the head called the Specific Anthropomorphic Mannequin (SAM), representing the top 10% of U.S. military recruits in 1989 and greatly underestimating the Specific Absorption Rate (SAR) for typical mobile phone users, especially children. A superior computer simulation certification process has been approved by the Federal Communications Commission (FCC) but is not employed to certify cell phones. In the United States, the FCC determines maximum allowed exposures. Many countries, especially European Union members, use the "guidelines" of International Commission on Non-Ionizing Radiation Protection (ICNIRP), a non governmental agency. Radiofrequency (RF) exposure to a head smaller than SAM will absorb a relatively higher SAR. Also, SAM uses a fluid having the average electrical properties of the head that cannot indicate differential absorption of specific brain tissue, nor absorption in children or smaller adults. The SAR for a 10-year old is up to 153% higher than the SAR for the SAM model. When electrical properties are considered, a child's head's absorption can be over two times greater, and absorption of the skull's bone marrow can be ten times greater than adults. Therefore, a new certification process is needed that incorporates different modes of use, head sizes, and tissue properties. Anatomically based models should be employed in revising safety standards for these ubiquitous modern devices and standards should be set by accountable, independent groups. PMID:21999884

Gandhi, Om P; Morgan, L Lloyd; de Salles, Alvaro Augusto; Han, Yueh-Ying; Herberman, Ronald B; Davis, Devra Lee

2011-10-14

161

Early Postnatal Sound Exposure Induces Lasting Neuronal Changes in the Inferior Colliculus of Senescence Accelerated Mice (SAMP8): A Morphometric Study on GABAergic Neurons and NMDA Expression  

Microsoft Academic Search

Senescence-acceleration-prone mice (SAMP8) provide a model to study the influence of early postnatal sound exposure upon the aging auditory midbrain. SAMP8 were exposed to a 9-kHz monotone of either 53- or 65-dB sound pressure level during the first 30 postnatal days, the neurons in the auditory midbrain responding selectively to 9 kHz were localized by c-fos immunohistochemistry and the following

Dietrich Ernst Lorke; Lai Yung Wong; Helen W. L. Lai; Paul W. F. Poon; Aiqun Zhang; Wood Yee Chan; David Tai Wai Yew

2003-01-01

162

Sub-diffraction-limited multilayer coatings for the 0.3-NA Micro-Exposure Tool for extreme ultraviolet lithography  

SciTech Connect

This manuscript discusses the multilayer coating results for the primary and secondary mirrors of the Micro Exposure Tool (MET): a 0.30-numerical aperture (NA) lithographic imaging system with 200 x 600 {micro}m{sup 2} field of view at the wafer plane, operating in the extreme ultraviolet (EUV) wavelength region. Mo/Si multilayers were deposited by DC-magnetron sputtering on large-area, curved MET camera substrates, and a velocity modulation technique was implemented to consistently achieve multilayer thickness profiles with added figure errors below 0.1 nm rms to achieve sub-diffraction-limited performance. This work represents the first experimental demonstration of sub-diffraction-limited multilayer coatings for high-NA EUV imaging systems.

Soufli, R; Hudyma, R M; Spiller, E; Gullikson, E M; Schmidt, M A; Robinson, J C; Baker, S L; Walton, C C; Taylor, J S

2007-01-03

163

Membrane Tension Accelerates Rate-limiting Voltage-dependent Activation and Slow Inactivation Steps in a Shaker Channel  

PubMed Central

A classical voltage-sensitive channel is tension sensitive—the kinetics of Shaker and S3–S4 linker deletion mutants change with membrane stretch (Tabarean, I.V., and C.E. Morris. 2002. Biophys. J. 82:2982–2994.). Does stretch distort the channel protein, producing novel channel states, or, more interestingly, are existing transitions inherently tension sensitive? We examined stretch and voltage dependence of mutant 5aa, whose ultra-simple activation (Gonzalez, C., E. Rosenman, F. Bezanilla, O. Alvarez, and R. Latorre. 2000. J. Gen. Physiol. 115:193–208.) and temporally matched activation and slow inactivation were ideal for these studies. We focused on macroscopic patch current parameters related to elementary channel transitions: maximum slope and delay of current rise, and time constant of current decline. Stretch altered the magnitude of these parameters, but not, or minimally, their voltage dependence. Maximum slope and delay versus voltage with and without stretch as well as current rising phases were well described by expressions derived for an irreversible four-step activation model, indicating there is no separate stretch-activated opening pathway. This model, with slow inactivation added, explains most of our data. From this we infer that the voltage-dependent activation path is inherently stretch sensitive. Simulated currents for schemes with additional activation steps were compared against datasets; this showed that generally, additional complexity was not called for. Because the voltage sensitivities of activation and inactivation differ, it was not possible to substitute depolarization for stretch so as to produce the same overall PO time course. What we found, however, was that at a given voltage, stretch-accelerated current rise and decline almost identically—normalized current traces with and without stretch could be matched by a rescaling of time. Rate-limitation of the current falling phase by activation was ruled out. We hypothesize, therefore, that stretch-induced bilayer decompression facilitates an in-plane expansion of the protein in both activation and inactivation. Dynamic structural models of this class of channels will need to take into account the inherent mechanosensitivity of voltage-dependent gating.

Laitko, Ulrike; Morris, Catherine E.

2004-01-01

164

Early Enriched Environment Exposure Protects Spatial Memory and Accelerates Amyloid Plaque Formation in APPSwe/PS1L166P Mice  

PubMed Central

Enriched environment exposure improves several aspects of cognitive performance in Alzheimer’s disease patients and in animal models and, although the role of amyloid plaques is questionable, several studies also assessed their response to enriched environment, with contrasting results. Here we report that rearing APPSwe/PS1L166P mice in an enriched environment since birth rescued the spatial memory impairment otherwise present at 6 months of age. At the same time, the exposure to the enriched environment caused a transient acceleration of plaque formation, while there was no effect on intracellular staining with the 6E10 antibody, which recognizes ?-amyloid, full length amyloid precursor protein and its C-terminal fragments. The anticipation of plaque formation required exposure during early development, suggesting an action within critical periods for circuits formation. On the other hand, chronic neuronal activity suppression by tetrodotoxin decreased the number of plaques without affecting intracellular amyloid. These results indicate that enriched environment exposure since early life has a protective effect on cognitive deterioration although transiently accelerates amyloid deposition. In addition, the effects of the enriched environment might be due to increased neuronal activity, because plaques were reduced by suppression of electrical signaling by tetrodotoxin.

Montarolo, Francesca; Parolisi, Roberta; Hoxha, Eriola; Boda, Enrica; Tempia, Filippo

2013-01-01

165

Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system  

PubMed Central

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (Enhydra lutris nereis) population growth: disease and resource limitation. This threatened population has struggled to recover despite protection, so we followed radio-tagged sea otters and evaluated infection with 2 disease-causing protozoal pathogens, Toxoplasma gondii and Sarcocystis neurona, to reveal risks that increased the likelihood of pathogen exposure. We identified patterns of pathogen infection that are linked to individual animal behavior, prey choice, and habitat use. We detected a high-risk spatial cluster of S. neurona infections in otters with home ranges in southern Monterey Bay and a coastal segment near San Simeon and Cambria where otters had high levels of infection with T. gondii. We found that otters feeding on abalone, which is the preferred prey in a resource-abundant marine ecosystem, had a very low risk of infection with either pathogen, whereas otters consuming small marine snails were more likely to be infected with T. gondii. Individual dietary specialization in sea otters is an adaptive mechanism for coping with limited food resources along central coastal California. High levels of infection with protozoal pathogens may be an adverse consequence of dietary specialization in this threatened species, with both depleted resources and disease working synergistically to limit recovery.

Johnson, Christine K.; Tinker, Martin T.; Estes, James A.; Conrad, Patricia A.; Staedler, Michelle; Miller, Melissa A.; Jessup, David A.; Mazet, Jonna A. K.

2009-01-01

166

Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system.  

PubMed

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (Enhydra lutris nereis) population growth: disease and resource limitation. This threatened population has struggled to recover despite protection, so we followed radio-tagged sea otters and evaluated infection with 2 disease-causing protozoal pathogens, Toxoplasma gondii and Sarcocystis neurona, to reveal risks that increased the likelihood of pathogen exposure. We identified patterns of pathogen infection that are linked to individual animal behavior, prey choice, and habitat use. We detected a high-risk spatial cluster of S. neurona infections in otters with home ranges in southern Monterey Bay and a coastal segment near San Simeon and Cambria where otters had high levels of infection with T. gondii. We found that otters feeding on abalone, which is the preferred prey in a resource-abundant marine ecosystem, had a very low risk of infection with either pathogen, whereas otters consuming small marine snails were more likely to be infected with T. gondii. Individual dietary specialization in sea otters is an adaptive mechanism for coping with limited food resources along central coastal California. High levels of infection with protozoal pathogens may be an adverse consequence of dietary specialization in this threatened species, with both depleted resources and disease working synergistically to limit recovery. PMID:19164513

Johnson, Christine K; Tinker, Martin T; Estes, James A; Conrad, Patricia A; Staedler, Michelle; Miller, Melissa A; Jessup, David A; Mazet, Jonna A K

2009-01-21

167

Language-Dependent Pitch Encoding Advantage in the Brainstem Is Not Limited to Acceleration Rates that Occur in Natural Speech  

ERIC Educational Resources Information Center

|Experience-dependent enhancement of neural encoding of pitch in the auditory brainstem has been observed for only specific portions of native pitch contours exhibiting high rates of pitch acceleration, irrespective of speech or nonspeech contexts. This experiment allows us to determine whether this language-dependent advantage transfers to…

Krishnan, Ananthanarayan; Gandour, Jackson T.; Smalt, Christopher J.; Bidelman, Gavin M.

2010-01-01

168

Health-based recommended occupational exposure limits for 1-methoxypropanol-2, 1-methoxypropylacetate-2, 2-methoxypropanol-1, 2-methoxypropylacetate-1. Met Nederlandstalige samenvatting  

Microsoft Academic Search

Since the beta-isomers are no commercial products and are only present as contaminants in the commercial products of PGME and PGMEA, with a maximum of 5%, the Working Group considers it irrelevant to advise a Occupational Exposure Limit (OEL). The Exposure Limits are recommended for products, containing not more than 5% of the beta-isomer. For com-PGME an OEL of 375

M. A. Maclaine Pont

1993-01-01

169

Evaluation of the practicability of limited sampling strategies for the estimation of mycophenolic acid exposure in Chinese adult renal recipients.  

PubMed

The immunosuppressive potential of mycophenolic acid (MPA) correlates well with MPA exposure [area under the concentration-time curve (AUC)]. Monitoring MPA AUC is important and helpful for maintaining the efficacy of mycophenolate mofetil while minimizing its side effects, but full MPA AUC monitoring is laborious, cost prohibitive, and impractical. Limited sampling strategies have been proposed as an alternative method for estimating MPA exposure. The objective of this study was to evaluate the practicability of different limited sampling strategies for the estimation of MPA exposure. A total of 56 pharmacokinetic profiles from 53 adult renal recipients were used to evaluate the practicability of 10 published models. Standard correlation and linear regression analysis were used to compare the estimated MPA AUCs and corresponding full MPA AUCs, and the percentage of profiles for which prediction error fell within +/-20% was also used to assess the practicability of these models. Agreement between the estimated MPA AUCs and full MPA AUCs was further tested by Bland and Altman analysis. The model, based on four sampling time points, used the formula AUC = 12.61 + 0.37 x C0.5 + 0.49 x C1 + 3.22 x C4 + 8.17 x C10, was superior to all other evaluated models, with the highest coefficient of determination (r = 0.88), a low percentage prediction error (2.79%), and good agreement according to Bland and Altman analysis. Prediction errors of 87.5% (49/56) of profiles were within 20%, which was the highest of all the models. This algorithm can be reliably used for estimating MPA exposure in adult renal transplant patients treated with cyclosporine as concomitant immunosuppressant. Another model based on the formula AUC = 8.22 + 3.16 x C0 + 0.99 x C1 + 1.33 x C2 + 4.18 x C4 also has acceptable predictive performance, and it may also be practical, especially in outpatient settings, in view of its distribution of time points. PMID:17898650

Zicheng, Yu; Xianghui, Wang; Peijun, Zhou; Da, Xu; Weixia, Zhang; Hongzhuan, Chen

2007-10-01

170

Evaluation of real-time techniques to measure hydrogen peroxide in air at the permissible exposure limit.  

PubMed

The major occupational concern from bio-decontamination of equipment using vapor phase hydrogen peroxide (VHP) generation systems is potential operator exposure outside the protective barrier from possible VHP leaks or accidental releases from the sealed piece of equipment during decontamination. For this reason, different real time monitoring techniques were evaluated to determine their ability to accurately measure VHP at concentrations ranging from 0.5 ppm to 5 ppm. The results of this laboratory evaluation suggest that two of the four methods evaluated (the ion mobility spectrometer [IMS] and Polytron) will approximate the National Institute for Occupational Safety and Health +/- 25% accuracy requirements for measuring the concentration of VHP at and near the Occupational Safety and Health Administration permissible exposure limit of 1.0 ppm. Over the range of 0.5 ppm to 5.1 ppm VHP, the IMS had an approximate pooled method accuracy of +/- 21%, while the Polytron had a pooled method accuracy of +/- 22%. However, both instruments had false readings when exposed to nominal concentrations of methanol, bleach, and sulfur dioxide. The two additional VHP monitoring techniques evaluated (the single point monitor [SPM] and Draeger tube) were unable to accurately measure the concentration of VHP when the relative humidity was below 20%. PMID:8865593

Puskar, M A; Plese, M R

1996-09-01

171

Ethical issues related to professional exposure of pregnant women in the medical field: monitoring and limiting effective dose.  

PubMed

The International Commission on Radiological Protection recommendations for occupational exposed pregnant women do not imply necessarily the complete avoidance of work with radiation or radioactive materials. Instead, a careful review of the exposure conditions, once the pregnancy is declared, as part of the exercise of the ICRP optimisation principle (based in a teleological ethics point of view) is suggested. The dose limitation (following a deontological ethics point of view) of the fetus/embryo is, however, not clearly well established as happens in the case of workers or members of the public. Also, the justification of practices (to continue to work or not with radiation or radioactive materials) is not clearly addressed in most national or international recommendations. An analysis of this justification (bearing in mind both teleological and deontological ethics) is examined in this work having in mind the best interest of the child-to-be as well as other existing social and economical factors. PMID:21068015

Santos, J A M; Nunes, R

2010-11-09

172

"Nuisance dust": unprotective limits for exposure to coal mine dust in the United States, 1934-1969.  

PubMed

I examine the dismissal of coal mine dust as a mere nuisance, not a potentially serious threat to extractive workers who inhaled it. In the 1930s, the US Public Health Service played a major role in conceptualizing coal mine dust as virtually harmless. Dissent from this position by some federal officials failed to dislodge either that view or the recommendation of minimal limitations on workplace exposure that flowed from it. Privatization of regulatory authority after 1940 ensured that miners would lack protection against respiratory disease. The reform effort that overturned the established misunderstanding in the late 1960s critically depended upon both the production of scientific findings and the emergence of a subaltern movement in the coalfields. This episode illuminates the steep challenges often facing advocates of stronger workplace health standards. PMID:23237176

Derickson, Alan

2012-12-13

173

Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system  

USGS Publications Warehouse

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (Enhydra lutris nereis) population growth: disease and resource limitation. This threatened population has struggled to recover despite protection, so we followed radio-tagged sea otters and evaluated infection with 2 disease-causing protozoal pathogens, Toxoplasma gondii and Sarcocystis neurona, to reveal risks that increased the likelihood of pathogen exposure. We identified patterns of pathogen infection that are linked to individual animal behavior, prey choice, and habitat use. We detected a high-risk spatial cluster of S. neurona infections in otters with home ranges in southern Monterey Bay and a coastal segment near San Simeon and Cambria where otters had high levels of infection with T. gondii. We found that otters feeding on abalone, which is the preferred prey in a resource-abundant marine ecosystem, had a very low risk of infection with either pathogen, whereas otters consuming small marine snails were more likely to be infected with T. gondii. Individual dietary specialization in sea otters is an adaptive mechanism for coping with limited food resources along central coastal California. High levels of infection with protozoal pathogens may be an adverse consequence of dietary specialization in this threatened species, with both depleted resources and disease working synergistically to limit recovery. ?? 2009 by The National Academy of Sciences of the USA.

Johnson, C. K.; Tinker, M. T.; Estes, J. A.; Conrad, P. A.; Staedler, M.; Miller, M. A.; Jessup, D. A.; Mazet, J. A. K.

2009-01-01

174

Radiolabeled microsphere technique in conscious subjects during acceleration exposures on the USAFAM centrifuge. Final report, August 1977-November 1978  

SciTech Connect

The methods used to apply the radiolabeled microsphere technique for the study of the effects of +Gz acceleration on regional blood flows are presented. A remote-control system designed to infuse suspensions of microspheres into the left atrium on conscious animals is outlined as is a device which allows the remote, sequential withdrawal of six blood samples. Results are presented which demonstrate that the cautious application of the radiolabeled microsphere technique using the outlined systems can produce good information about the effects of +Gz acceleration on regional blood flows.

Laughlin, M.H.; Jaggars, J.L.

1980-03-01

175

Limits of NbTi and Nb3Sn, and Development of W&R Bi-2212 HighField Accelerator Magnets  

SciTech Connect

NbTi accelerator dipoles are limited to magnetic fields (H)of about 10 T, due to an intrinsic upper critical field(Hc2) limitationof 14 T. To surpass this restriction, prototype Nb3Sn magnets are beingdeveloped which have reached 16 T. We show that Nb3Sn dipole technologyis practically limited to 17 to 18 T due to insufficient high fieldpinning, and intrinsically to 20 to 22 T due to Hc2 limitations.Therefore, to obtain magnetic fields approaching 20 T and higher, amaterial is required with a higher Hc2 and sufficient high field pinningcapacity. A realistic candidate for this purpose is Bi-2212, which isavailable in roundwires and sufficient lengths for the fabrication ofcoils based on Rutherford-type cables. We initiated a program to developthe required technology to construct accelerator magnets from'windand-react' (W&R) Bi-2212 coils. We outline the complicationsthat arise through the use of Bi-2212, describe the development paths toaddress these issues, and conclude with the design of W&R Bi-2212sub-scale magnets.

Godeke, A.; Cheng, D.; Dietderich, D.R.; Ferracin, P.; Prestemon,S.O.; Sabbi, G.; Scanlan, R.M.

2006-12-01

176

Exposure to high or low glucose levels accelerates the appearance of markers of endothelial cell senescence and induces dysregulation of nitric oxide synthase.  

PubMed

To test the hypothesis that aging impairs endothelial cell response to glucose stress, we utilized a human umbilical vein endothelial cell in vitro model in which clinically relevant concentrations of normal (5.5mM), high (25mM), and low (1.5mM) glucose were tested. With advancing population doubling, exposure to normal glucose gradually decreased endothelial nitric oxide synthase expression and activity, resulting in slow, progressive development of markers of cell senescence (by population doubling level [PDL] 44). High or low glucose treatment accelerated the appearance of markers of senescence (by ~PDL 35) along with declines in endothelial nitric oxide synthase expression and activity. Human umbilical vein endothelial cells exposed to alternating low and high glucose gave even more rapid acceleration in the appearance of markers of senescence (by ~PDL 18) and reduction in endothelial nitric oxide synthase levels. Thus, exposure to low and high glucose induces earlier appearance of markers of endothelial cell senescence and dysregulation of the nitric oxide synthase gene and protein expression and function. These findings will help to elucidate endothelial dysfunction associated with glucose intolerance and improve future therapy for diabetic seniors. PMID:23585419

Rogers, Steven C; Zhang, Xiaomin; Azhar, Gohar; Luo, Shaoke; Wei, Jeanne Y

2013-04-12

177

Throwing the baby out with the bath water? Occupational hygienists' views on the revised dutch system for occupational exposure limits.  

PubMed

In 2007, the Dutch Working Conditions Act was revised with the goal to decrease the regulatory burden, and to open up for company-specific solutions of establishing a safe and healthy work environment. One tool geared towards company-specific solutions is the compilation of the Arbocatalogs, which are company or sector-level collections of safe working methods and guidelines developed both by employers and employees. The revision also introduced a new occupational exposure limit (OEL) system in the Netherlands. This system encompasses two kinds of OELs: private and public. Private OELs are to be derived by the industry, while public OELs are issued by the Ministry of Social Affairs and Employment. With this change, the majority of the previously set Dutch OELs were removed, as the substances in question now are falling under the private realm. The motivations, expectations, and practical impacts of these revisions have been investigated through interviews with stakeholder organizations and a questionnaire study targeted at occupational hygienists. The questionnaire results show that although the Arbocatalogs seem to be relatively well received, a majority of the Dutch occupational hygienists are still relatively negative to the changes. There is a fear that private OELs will be less scientifically robust than public OELs and that the lack of robustness will have a negative impact on the field of occupational hygiene as a whole. PMID:23253359

Schenk, Linda; Palmen, Nicole Gm

2012-12-18

178

Accelerated Biodegradation of Veterinary Antibiotics in Agricultural Soil following Long-Term Exposure, and Isolation of a Sulfamethazine-degrading sp.  

PubMed

The World Health Organization has identified antibiotic resistance as one of the top three threats to global health. There is concern that the use of antibiotics as growth promoting agents in livestock production contributes to the increasingly problematic development of antibiotic resistance. Many antibiotics are excreted at high rates, and the land application of animal manures represents a significant source of environmental exposure to these agents. To evaluate the long-term effects of antibiotic exposure on soil microbial populations, a series of field plots were established in 1999 that have since received annual applications of a mixture of sulfamethazine (SMZ), tylosin (TYL), and chlortetracycline (CTC). During the first 6 yr (1999-2004) soils were treated at concentrations of 0, 0.01 0.1, and 1.0 mg kg soil, in subsequent years at concentrations of 0, 0.1, 1.0, and 10 mg kg soil. The lower end of this concentration range is within that which would result from an annual application of manure from medicated swine. Following ten annual applications, the fate of the drugs in the soil was evaluated. Residues of SMZ and TYL, but not CTC were removed much more rapidly in soil with a history of exposure to 10 mg/kg drugs than in untreated control soil. Residues of C-SMZ were rapidly and thoroughly mineralized to CO in the historically treated soils, but not in the untreated soil. A SMZ-degrading sp. was isolated from the treated soil. Overall, these results indicate that soil bacteria adapt to long-term exposure to some veterinary antibiotics resulting in sharply reduced persistence. Accelerated biodegradation of antibiotics in matrices exposed to agricultural, wastewater, or pharmaceutical manufacturing effluents would attenuate environmental exposure to antibiotics, and merits investigation in the context of assessing potential risks of antibiotic resistance development in environmental matrices. PMID:23673752

Topp, Edward; Chapman, Ralph; Devers-Lamrani, Marion; Hartmann, Alain; Marti, Romain; Martin-Laurent, Fabrice; Sabourin, Lyne; Scott, Andrew; Sumarah, Mark

179

Price To Be Paid for Two-Metal Catalysis: Magnesium Ions That Accelerate Chemistry Unavoidably Limit Product Release from a Protein Kinase  

PubMed Central

Incorporation of divalent metal ions into an active site is a fundamental catalytic tool used by diverse enzymes. Divalent cations are used by protein kinases to both stabilize ATP binding and accelerate chemistry. Kinetic analysis establishes that Cyclin-dependent kinase 2 (CDK2) requires simultaneous binding of two Mg2+ ions for catalysis of phosphoryl transfer. This tool, however, comes with a price: the rate-acceleration effects are opposed by an unavoidable rate-limiting consequence of the use of two Mg2+ ions by CDK2. The essential metal ions stabilize ADP product binding and limit the overall rate of the reaction. We demonstrate that product release is rate limiting for activated CDK2 and evaluate the effects of the two catalytically essential Mg2+ ions on the stability of the ADP product within the active site. We present two new crystal structures of CDK2 bound to ADP showing how the phosphate groups can be coordinated by either one or two Mg2+ ions, with the occupancy of one site in a weaker equilibrium. Molecular dynamics simulations indicate that ADP phosphate mobility is more restricted when ADP is coordinated by two Mg2+ ions compared to one. The structural similarity between the rigid ADP·2Mg product and the cooperatively assembled transition state provides a mechanistic rational for the rate-limiting ADP release that is observed. We demonstrate that although the simultaneous binding of two Mg2+ ions is essential for efficient phosphoryl transfer, the presence of both Mg2+ ions in the active site also cooperatively increases ADP affinity and opposes its release. Evolution of protein kinases must have involved careful tuning of the affinity for the second Mg2+ ion in order to balance the needs to stabilize the chemical transition state and allow timely product release. The link between Mg2+ site affinity and activity presents a chemical handle that may be used by regulatory factors as well as explain some mutational effects.

2012-01-01

180

Accelerator mass spectrometry in biomedical dosimetry: relationship between low-level exposure and covalent binding of heterocyclic amine carcinogens to DNA.  

PubMed Central

Accelerator mass spectrometry (AMS) is used to determine the amount of carcinogen covalently bound to mouse liver DNA (DNA adduct) following very low-level exposure to a 14C-labeled carcinogen. AMS is a highly sensitive method for counting long-lived but rare cosmogenic isotopes. While AMS is a tool of importance in the earth sciences, it has not been applied in biomedical research. The ability of AMS to assay rare isotope concentrations (10Be, 14C, 26Al, 41Ca, and 129I) in microgram amounts suggests that extension to the biomedical sciences is a natural and potentially powerful application of the technology. In this study, the relationship between exposure to low levels of 2-amino-3,8-dimethyl[2-14C]imidazo[4,5-f]quinoxaline and formation of DNA adducts is examined to establish the dynamic range of the technique and the potential sensitivity for biological measurements, as well as to evaluate the relationship between DNA adducts and low-dose carcinogen exposure. Instrument reproducibility in this study is 2%; sensitivity is 1 adduct per 10(11) nucleotides. Formation of adducts is linearly dependent on dose down to an exposure of 500 ng per kg of body weight. With the present measurements, we demonstrate at least 1 order of magnitude improvement over the best adduct detection sensitivity reported to date and 3-5 orders of magnitude improvement over other methods used for adduct measurement. An additional improvement of 2 orders of magnitude in sensitivity is suggested by preliminary experiments to develop bacterial hosts depleted in radiocarbon. Expanded applications involving human subjects, including clinical applications, are now expected because of the great detection sensitivity and small sample size requirements of AMS.

Turteltaub, K W; Felton, J S; Gledhill, B L; Vogel, J S; Southon, J R; Caffee, M W; Finkel, R C; Nelson, D E; Proctor, I D; Davis, J C

1990-01-01

181

Accelerating machines: a review  

Microsoft Academic Search

This paper presents an overview of accelerating machines. We begin by exploring the history of the accelerating machine model and the potential power that it provides. We look at a number of computations that could be performed with an accelerating machine, and review various possible implementation methods that have been proposed. Finally, we expose the limitations of accelerating machines and

Robert Fraser; Selim G. Akl

2008-01-01

182

Association of years of occupational quartz exposure with spirometric airflow limitation in Norwegian men aged 30–46 years  

Microsoft Academic Search

BACKGROUNDThe association between occupational quartz exposure and ventilatory function was investigated in men in a general population after adjusting for other potential determinants of outcome.METHODSAll eligible men aged 30–46 years living in western Norway (n = 45 380) were invited to a cross sectional community survey. This included a self administered questionnaire (with respiratory symptoms, smoking habits and occupational exposures),

Sjur Humerfelt; Geir E Eide; Amund Gulsvik

1998-01-01

183

Postnatal exposure to chromium through mother's milk accelerates follicular atresia in F1 offspring through increased oxidative stress and depletion of antioxidant enzymes.  

PubMed

Hexavalent chromium, CrVI, is a heavy metal endocrine disruptor, known as a mutagen, teratogen, and a group A carcinogen. Environmental contamination with CrVI, including drinking water, has been increasing in more than 30 cities in the United States. CrVI is rapidly converted to CrIII intracellularly, and CrIII can cause DNA strand breaks and cancer or apoptosis through different mechanisms. Our previous study demonstrated that lactational exposure to chromium results in a delay or arrest in follicle development and a decrease in steroid hormone levels in F1 female rats, both of which are mitigated (partial inhibition) by vitamin C. The current study tested the hypothesis that lactational exposure to CrIII accelerates follicle atresia in F1 offspring by increasing reactive oxygen species (ROS) and decreasing cellular antioxidants. Results showed that lactational exposure to CrIII dose-dependently increased follicular atresia and decreased steroidogenesis in postnatal day 25, 45, and 65 rats. Vitamin C mitigated or inhibited the effects of CrIII at all doses. CrIII increased hydrogen peroxide and lipid hydroperoxide in plasma and ovary; decreased the antioxidant enzymes (AOXs) GPx1, GR, SOD, and catalase; and increased glutathione S-transferase in plasma and ovary. To understand the effects of CrVI on ROS and AOXs in granulosa (GC) and theca (TC) cell compartments in the ovary, ROS levels and mRNA expression of cytosolic and mitochondrial AOXs, such as SOD1, SOD2, catalase, GLRX1, GSTM1, GSTM2, GSTA4, GR, TXN1, TXN2, TXNRD2, and PRDX3, were studied in GCs and TCs and in a spontaneously immortalized granulosa cell line (SIGC). Overall, CrVI downregulated each of the AOXs; and vitamin C mitigated the effects of CrVI on these enzymes in GCs and SIGCs, but failed to mitigate CrVI effects on GSTM1, GSTM2, TXN1, and TXN2 in TCs. Thus, these data for the first time reveal that lactational exposure to CrIII accelerated follicular atresia and decreased steroidogenesis in F1 female offspring by altering the ratio of ROS and AOXs in the ovary. Vitamin C is able to protect the ovary from CrIII-induced oxidative stress and follicle atresia through protective effects on GCs rather than TCs. PMID:23470461

Stanley, Jone A; Sivakumar, Kirthiram K; Nithy, Thamizh K; Arosh, Joe A; Hoyer, Patricia B; Burghardt, Robert C; Banu, Sakhila K

2013-03-01

184

Non-cancer health risk assessment from exposure to cyanide by resident adults from the mining operations of Bogoso Gold Limited in Ghana.  

PubMed

Cyanide is a very toxic chemical that is used to extract gold from its ores. Wastewaters from gold mining companies such as Bogoso Gold Limited (BGL) contain cyanide and other potentially toxic chemicals that have adverse effects on human beings and aquatic organisms. This study was conducted to evaluate the human health risk assessment from exposure to free cyanide via oral and dermal contact of surface/underground water by resident adults within the concession of Bogoso Gold Limited. The chronic non-cancer health risk from exposure to cyanide in River Bogo Upstream is 230 and 43 (by Central Tendency Exposure (CTE) parameters respectively). This means that approximately 230 and 43 resident adults are likely to suffer diseases related to cyanide intoxication via oral and dermal contact respectively. For chronic exposure to River Bogo Downstream by resident adults, the non-cancer health risks are: 0.031 and 0.57 via oral and dermal contact for CTE parameters respectively, which also means that, the non-cancer health risks associated with cyanide intoxication is negligible as the hazard index is less than 1.0 via oral and dermal contacts respectively. The results showed that health risk for acute exposure to cyanide by the resident adults is very high. Hence the residents attribute most of the unexplained deaths in the communities to accidental ingestion and dermal contact of cyanide water. PMID:16897533

Obiri, S; Dodoo, D K; Okai-Sam, F; Essumang, D K

2006-07-01

185

Long-term perchloroethylene exposure: a limited meta-analysis of neurobehavorial deficits in occupationally and residentially exposed groups  

EPA Science Inventory

The literature concerning the neurobehavioral and neurophysiological effects of long-term exposure to perchloroethylene (PERC) in humans was meta-analyzed to provide a quantitative review and synthesis. The useable data base from this literature comprised studies reporting effec...

186

Influence of background exposure on detection and determination limits for a TL dosimetry system based on LiF:Mg,Cu,P(GR-200A).  

PubMed

Thermoluminescence dosemeters are widely used to monitor personal doses. For these low dose range applications, it is important to determine the detection limit L(D) and the determination limit L(Q) of the dosimetric system. The influence of background exposure on these limits for LiF:Mg,Cu,P(GR-200A) based TL dosimetry was investigated. Both the conventional analysis and the glow curve analysis methods were used to determinate these limits. The detection limit L(D) was compared with the recording level and the investigation level. A systematic error can occur in the occupational dose evaluation when the detection limit L(D) is more than the recording level. It was found that the L(D) of the dosimetric system-based LiF:Mg,Cu,P(GR-200A) was less than the recording level for exposure time tau > or = 10 days considering an annual dose limit of 1 mSv for the public recommended in ICRP Publication 60. PMID:12382732

Tang, K Y; Liu, B X; Zhu, H Y; Wang, Y C; Shen, W X

2002-01-01

187

Effects of food-cue exposure on dieting-related goals: A limitation to counteractive-control theory  

Microsoft Academic Search

The present study investigated the effects of exposure to a food cue on the self-reported importance of dieting in those with low, medium, and high levels of dietary restraint. The results indicated that exposure to a food cue bolstered dieting-related goals in those who were low in dietary restraint but had no effect on the importance of dieting-related goals for

Jennifer S. Coelho; Janet Polivy; C. Peter Herman; Patricia Pliner

2008-01-01

188

WOOD DUST EXPOSURE DURING FURNITURE MANUFACTURE—RESULTS FROM AN AUSTRALIAN SURVEY AND CONSIDERATIONS FOR THRESHOLD LIMIT VALUE DEVELOPMENT  

Microsoft Academic Search

A survey of time-weighted average (TWA) personal inhalable dust exposures for woodworkers in 15 Australian furniture factories was undertaken. There was significant variation in the individual dust measurements with mean exposures of 3.2, 5.2, and 3.5?mg\\/m for wood machinists, cabinetmakers, and chair framemakers, respectively. Hardwoods, softwoods, and reconstituted woods are used in the industry, but only minor differences in mean

Dino L. Pisaniello; Karen E. Connell; Luciano Muriale

1991-01-01

189

Quantification of print, radio and television exposure among previous blood donors in Kenya: an opportunity for encouraging repeat donation in a resource-limited setting?  

PubMed

Blood services in sub-Saharan Africa experience blood shortages and low retention of voluntary, non-remunerated donors. To boost collections by encouraging repeat donations, the Kenya National Blood Transfusion Service is exploring the likelihood of reaching previous donors through targeted print, radio and television advertising. We analysed data from a national AIDS Indicator Survey to determine whether previous donors have significant exposure to media. Respondents reporting history of blood donation had significantly higher exposure to print, radio and television media than those without history of blood donation. Targeted media campaigns encouraging repeat donation are likely to reach previous donors even in resource-limited settings. PMID:20598106

Basavaraju, S V; Mwangi, J; Kellogg, T A; Odawo, L; Marum, L H

2010-10-01

190

Quantitative property-property relationships for computing occupational exposure limits and vapour hazard ratios of organic solvents.  

PubMed

Vapour Hazard Ratio (VHR) is used in solvent substitution to select the best replacement option regarding overexposure potential of solvents. However, VHR calculations are limited by the availability of Occupational Exposure Limits (OELs). The overall objective of this study was to develop quantitative property-property relationship (QPPR) approaches for computing OELs, in view of supporting the derivation of VHRs for solvents without OELs. QPPRs were developed for estimating OELs using a database of 88 solvents which have health-based Time-Weighted Average (TWA) OELs published by the American Conference of Governmental Industrial Hygienists (ACGIH). Three surrogates of biotic lipid : air partition coefficients [n-octanol : air (K(oa)), olive oil : air (K(oila)) and fat : air (K(fa))] were selected for evaluating the descriptive/predictive relationship with OELs for solvents with local modes of action. For solvents with systemic modes of action, the prediction of OEL needs to consider quantitative differences in toxicokinetics (i.e. kinetic variability factor, KVF) and toxicological potency (i.e. effective internal concentration, EIC). The n-octanol : water (K(ow)), the oil : water (K(oilw)) and the fat : water (K(fw)) partition coefficients were selected for evaluating the relationship with EICs. For local modes of action, K(oa) is the most accurate predictor of OELs [OEL (ppm) = 10(((-0.45 x log K(oa)) + 3.65)); n = 21, r²= 0.71, PRESS/SSY = 0.36, F = 45.5 with p < 0.001] and the mean (±SD) (range) of the recommended to predicted OELs was 1.04 ± 0.61 (0.2-2.5). For systemic modes of action, KVFs and EICs vary in a range from 0.73 to 41.4 µmol L?¹ and 1.20-848 µmol L?¹, respectively. K(ow) is an accurate predictor of calculated EICs [EIC (µmol L?¹) = 10 (((-1.16 x log K(ow)) + 3.65)); n = 27, r²= 0.88, PRESS/SSY = 0.12, F = 181 with p < 0.001] and 50% of the predicted OEL values were within a factor of two of the recommended TWA OELs. Overall, 61% and 87% of the predicted VHRs were within a factor of two and five, respectively, of the calculated VHRs. The QPPR models developed in this study represent potentially useful tools for estimating provisional OELs for solvents lacking such guideline values. These provisional OELs are developed only to support initial estimations of VHR for dealing with the challenge of solvent substitution where relative values rather than absolute values of OEL and vapour pressure guide the hygienist in making pragmatic decisions for managing occupational health hazards. PMID:21120751

Debia, M; Krishnan, K

2010-10-01

191

Degradation of ZnO-Based Window Layers for Thin-Film CIGS by Accelerated Stress Exposures  

SciTech Connect

The reliability of ZnO-based window layer for CuInGaSe{sub 2} (CIGS) solar cells was investigated. Samples of RF magnetron-sputtered, single-layer intrinsic and Al-doped ZnO and their combined bilayer on glass substrates were exposed in a weatherometer (WOM) and damp heat (DH) conditions with or without acetic acid vapor. Some preliminary samples of single-layer Al-doped Zn{sub 1-x}Mg{sub x}O (ZMO) alloy, a potential replacement for Al:ZnO with a wider bandgap, were also evaluated in the DH. The Al-doped ZnO and ZMO films showed irreversible loss in the conducting properties, free carrier mobility, and characteristic absorption band feature after <500-h DH exposure, with the originally clear transparent films turned into white hazy insulating films and the degradation rate follows the trend of (DH + acetic acid) > DH > WOM. The degradation rate was also reduced by higher film thickness, higher deposition substrate temperature, and dry-out intervals. The results of X-ray diffraction analysis indicate that the ZnO-based films underwent structural degeneration by losing their highly (002) preferential orientation with possible transformation from hexagonal into cubic and formation of Zn(OH){sub 2}. Periodic optical micro-imaging observations suggested a temporal process that involves initial hydrolysis of the oxides at sporadic weak spots, swelling and popping of the hydrolyzed spots due to volume increase, segregation of hydrolyzed regions causing discontinuity of electrical path, hydrolysis of the oxide-glass interface, and finally, formation of insulating oxides/hydroxides with visible delamination over larger areas.

Pern, F. J.; Noufi, R.; To, B.; DeHart, C.; Li, X.; Glick, S. H.

2008-01-01

192

Hepatotoxic effects of solvent exposure around permissible limits and alcohol consumption in printers over a 4-year period  

Microsoft Academic Search

Two field studies were carried out in 1987 and 1991 in order to evaluate the effect of chronic exposure to solvent mixture on liver enzyme patterns. The results in 33 workers who participated in both studies and had complete sets of data are presented. The magnitude of chemical workload was assessed by means of ambient air monitoring and biomonitoring of

Michael Nasterlack; Gerhard Triebig; Ottmar Stelzer

1994-01-01

193

Estimate of the potential costs of guidelines limiting public exposure to radiofrequency radiation from broadcast sources. Volume 1: report. Volume 2: Appendix, Parts 1 and 2. Final report  

Microsoft Academic Search

The purpose of this study is to estimate the cost of a federal guidance proposed by the U.S. Environmental Protection Agency (EPA) limiting public exposure to radiofrequency (RF) radiation from the broadcast industry--the 9000 AM and FM radio stations and 1000 VHF-TV and UHF-TV broadcast stations in the U.S. The Lawrence Livermore National Laboratory developed models that estimate a variety

Hall

1985-01-01

194

Revision of French Occupational Exposure Limits of Asbestos and recommendation of measurement method: Can the dimensional characteristics of the asbestos fibres (long, thin, short) be taken into account?  

Microsoft Academic Search

In France, the current regulations on occupational exposure to asbestos fibres take into account fibres (FRp: fibres measured for industrial hygiene) with the following dimensions: L > 5 ?m, D < 3 ?m and L\\/D > 3 where L is the length and D the diameter of the fibre. The limit value is set at 0.1 f\\/cm for 1 hour. By definition short

M. El Yamani; G. Boulanger; E. Nerrière-Catelinois; A. Paillat; H. Modelon; A. Soyez; F. Paquet; S. Binet; P. Brochard

2011-01-01

195

Limiting the Amount and Duration of Antigen Exposure During Priming Increases Memory T Cell Requirement for Costimulation During Recall  

PubMed Central

Donor-reactive memory T cells can play an important role in mediating graft rejection following transplantation. Transplant recipients acquire donor-reactive memory T cells not only through prior sensitization with alloantigens, but also through previous exposure to environmental pathogens that are cross-reactive with allogeneic peptide:MHC complexes. Current dogma suggests that most, if not all, memory T cell responses are independent of the requirement for CD28 and/ or CD154/CD40-mediated costimulation in order to mount a recall response. However, heterogeneity among memory T cells is increasingly being appreciated, and one important factor known to impact the function and phenotype of antigen-specific T cell responses is the amount/duration of antigen exposure. Importantly, the impact of antigen exposure on development of costimulation independence is currently unknown. Here, we interrogated the effect of decreased antigen amount/duration during priming on the ability of donor-reactive memory T cells to mediate costimulation blockade-resistant rejection during a recall response following transplantation in a murine model. Recipients possessing donor-reactive memory T cell responses that were generated under conditions of reduced antigen exposure exhibited similar frequencies of antigen-specific T cells at day 30 post infection, but, strikingly, failed to mediate costimulation blockade-resistant rejection following challenge with an OVA-expressing skin graft. Thus, these data demonstrate the amount/ duration of antigen exposure is a critical factor in determining memory T cells' relative requirement for costimulation during the recall response following transplantation.

Floyd, Tamara L.; Koehn, Brent H.; Kitchens, William H.; Robertson, Jennifer M.; Cheeseman, Jennifer A.; Stempora, Linda; Larsen, Christian P.; Ford, Mandy L.

2011-01-01

196

Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system  

Microsoft Academic Search

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (Enhydra lutris nereis) population growth: disease and resource limitation. This threatened population has struggled to recover

Christine K. Johnson; Martin T. Tinker; James A. Estes; Patricia A. Conrad; Michelle Staedler; Melissa A. Miller; David A. Jessup; Jonna A. K. Mazet

2009-01-01

197

Neonatal UVB exposure accelerates melanoma growth and enhances distant metastases in Hgf-Cdk4(R24C) C57BL/6 mice.  

PubMed

Genetically engineered mouse models offer new opportunities to experimentally investigate the impact of UV on melanoma pathogenesis. Here we irradiated a cohort of newborn 15 Hgf-Cdk4(R24C) mice on the pigmented C57BL/6 background with one erythemogenic dose of 6 kJ/m(2) UVB and compared the development of nevi and melanoma with a cohort of 30 untreated Hgf-Cdk4(R24C) mice. Neonatal UVB exposure decreased the latency and accelerated the growth of primary melanomas resulting in a significantly decreased time from melanoma onset to melanoma-related death (61 days vs. 96 days). Interestingly, we did not observe differences in the development of melanocytic nevi. Histopathological investigations revealed that UVB irradiation shifted the spectrum of melanomas toward a more aggressive phenotype with increased tumor cell proliferation, invasive growth and enhanced angiogenesis. Accordingly, we observed distal melanoma metastases in the lungs more frequently in the UV-irradiated than in the untreated cohort of Hgf-Cdk4(R24C) mice (73% vs. 47%). UVB-induced melanomas only contained very few infiltrating immune cells and expressed very low levels of proinflammatory chemokines. Taken together, our results demonstrate that neonatal UVB exposure promoted the early appearance of rapidly enlarging primary melanomas in Hgf-Cdk4(R24C) C57BL/6 mice which showed enhanced invasive and metastatic behaviour without a persistent tumor-associated inflammatory response. The preferential impact of UVB irradiation on the progression of melanoma without an effect on the development of nevi supports the hypothesis that the molecular targets of UVB are involved in bypassing the proliferative arrest of transformed melanocytes without alerting a cellular immune response. PMID:21207411

Gaffal, Evelyn; Landsberg, Jennifer; Bald, Tobias; Sporleder, Alexander; Kohlmeyer, Judith; Tüting, Thomas

2011-04-21

198

In vivo comparison of epithelial responses for S-8 versus JP-8 jet fuels below permissible exposure limit  

Microsoft Academic Search

This study was designed to characterize and compare the pulmonary effects in distal lung from a low-level exposure to jet propellant-8 fuel (JP-8) and a new synthetic-8 fuel (S-8). It is hypothesized that both fuels have different airway epithelial deposition and responses. Consequently, male C57BL\\/6 mice were nose-only exposed to S-8 and JP-8 at average concentrations of 53mg\\/m3 for 1h\\/day

Simon S. Wong; Jason Vargas; Alana Thomas; Cindy Fastje; Michael McLaughlin; Ryan Camponovo; R. Clark Lantz; Jeffrey Heys; Mark L. Witten

2008-01-01

199

Health-based Occupational Exposure Limits for High Molecular Weight Sensitizers: How Long is the Road We Must Travel?  

Microsoft Academic Search

In this paper pitfalls in risk assessment for high molecular weight allergens, which can cause typical Type I\\/IgE-mediated respiratory allergy, are discussed. The major pitfalls seem to be that no agreement exists on the preferential end point that should be used in risk assessment. As a result, it is unclear which exposure-response relationship should be considered. In addition, there is

DICK HEEDERIK; PETER S. THORNE; GERT DOEKES

2002-01-01

200

Work to save dose: contrasting effective dose rates from radon exposure in workplaces and residences against the backdrop of public and occupational limits  

SciTech Connect

Office workers are exposed to radon while at work and at home. Though there has been a multitude of studies reporting the measurements of radon concentrations and potential lung and effective doses associated with radon and progeny exposure in homes, similar studies on the concentrations and subsequent effective dose rates in the non-mine workplaces are lacking. Additionally, there are few, if any, comparative analyses of radon exposures at more 'typical' workplace with residential exposures within the same county. The purposes of this study were to measure radon concentrations in office and residential spaces in the same county and explore the radiation dose implications. Sixty-five track-etch detectors were deployed in office spaces and 47 were deployed in residences, all within Los Alamos County, New Mexico, USA. The sampling periods for these measurements were generally about three months. The measured concentrations were used to calculate and compare effective dose rates resulting from exposure while at work and at home. Results showed that full-time office workers receive on average about 8 times greater exposure at home than while in the office (2.3 mSv yr-! versus 0.3 mSv yr-!). The estimated effective dose rate for a more homebound person was about 3 mSv yr-!. Estimating effective doses from background radon exposure in the same county as Los Alamos National Laboratory, with thousands of'radiological workers,' highlights interesting contrasts in radiation protection standards that span public and occupational settings. For example, the effective dose rate from background radon exposure in unregulated office spaces ranged up to 1.1 mSv yr-!, which is similar to the 1 mSv yr-! threshold for regulation ofa 'radiological worker,' as defined in the Department of Energy regulations for occupational exposure. Additionally, the estimated average effective dose total of> 3 mSv yf! from radon background exposure in homes stands in contrast to the 0.1 mSv yr-! air pathway effective public dose limit regulated by the Environmental Protection Agency for radioactive air emissions.

Whicker, Jeffrey J [Los Alamos National Laboratory; Mcnaughton, Michael W [Los Alamos National Laboratory

2009-01-01

201

Laser selection based on maximum permissible exposure limits for visible and middle-near infrared repetitively pulsed lasers.  

SciTech Connect

The Maximum Permissible Exposure (MPE) is central to laser hazard analysis and is in general a function of the radiant wavelength. The selection of a laser for a particular application may allow for flexibility in the selection of the radiant wavelength. This flexibility would allow the selection of a particular laser based on the MPE and the hazards associated with that radiant wavelength. The Calculations of the MPEs for various laser wavelength ranges are presented. Techniques for determining eye safe viewing distances for both aided and unaided viewing and the determination of flight hazard distances are presented as well.

Augustoni, Arnold L.

2004-03-01

202

In vivo comparison of epithelial responses for S-8 versus JP-8 jet fuels below permissible exposure limit.  

PubMed

This study was designed to characterize and compare the pulmonary effects in distal lung from a low-level exposure to jet propellant-8 fuel (JP-8) and a new synthetic-8 fuel (S-8). It is hypothesized that both fuels have different airway epithelial deposition and responses. Consequently, male C57BL/6 mice were nose-only exposed to S-8 and JP-8 at average concentrations of 53mg/m(3) for 1h/day for 7 days. A pulmonary function test performed 24h after the final exposure indicated that there was a significant increase in expiratory lung resistance in the S-8 mice, whereas JP-8 mice had significant increases in both inspiratory and expiratory lung resistance compared to control values. Neither significant S-8 nor JP-8 respiratory permeability changes were observed compared to controls, suggesting no loss of epithelial barrier integrity. Morphological examination and morphometric analysis of airway tissue demonstrated that both fuels showed different patterns of targeted epithelial cells: bronchioles in S-8 and alveoli/terminal bronchioles in JP-8. Collectively, our data suggest that both fuels may have partially different deposition patterns, which may possibly contribute to specific different adverse effects in lung ventilatory function. PMID:18930109

Wong, Simon S; Vargas, Jason; Thomas, Alana; Fastje, Cindy; McLaughlin, Michael; Camponovo, Ryan; Lantz, R Clark; Heys, Jeffrey; Witten, Mark L

2008-09-27

203

A Solid state accelerator  

SciTech Connect

We present a solid state accelerator concept utilizing particle acceleration along crystal channels by longitudinal electron plasma waves in a metal. Acceleration gradients of order 100 GV/cm are theoretically possible, but channeling radiation limits the maximum attainable energy to 10/sup 5/ TeV for protons. Beam dechanneling due to multiple scattering is substantially reduced by the high acceleration gradient. Plasma wave dissipation and generation in metals are also discussed.

Chen, P.; Noble, R.J.

1986-11-06

204

Recovery of NMDA receptor currents from MK-801 blockade is accelerated by Mg2+ and memantine under conditions of agonist exposure  

PubMed Central

MK-801 is a use-dependent NMDA receptor open channel blocker with a very slow off-rate. These properties can be exploited to ‘pre-block’ a population of NMDARs, such as synaptic ones, enabling the selective activation of a different population, such as extrasynaptic NMDARs. However, the usefulness of this approach is dependent on the stability of MK-801 blockade after washout. We have revisited this issue, and confirm that recovery of NMDAR currents from MK-801 blockade is enhanced by channel opening by NMDA, and find that it is further increased when Mg2+ is also present. In the presence of Mg2+, 50% recovery from MK-801 blockade is achieved after 10? of 100 ?M NMDA, or 30? of 15 ?M NMDA exposure. In Mg2+-free medium, NMDA-induced MK-801 dissociation was found to be much slower. Memantine, another PCP-site antagonist, could substitute for Mg2+ in accelerating the unblock of MK-801 in the presence of NMDA. This suggests a model whereby, upon dissociation from its binding site in the pore, MK-801 is able to re-bind in a process antagonized by Mg2+ or another PCP-site antagonist. Finally we show that even when all NMDARs are pre-blocked by MK-801, incubation of neurons with 100 ?M NMDA in the presence of Mg2+ for 2.5 h triggers sufficient unblocking to kill >80% of neurons. We conclude that while synaptic MK-801 ‘pre-block’ protocols are useful for pharmacologically assessing synaptic vs. extrasynaptic contributions to NMDAR currents, or studying short-term effects, it is problematic to use this technique to attempt to study the effects of long-term selective extrasynaptic NMDAR activation. This article is part of the Special Issue entitled ‘Glutamate Receptor-Dependent Synaptic Plasticity’.

McKay, Sean; Bengtson, C. Peter; Bading, Hilmar; Wyllie, David J.A.; Hardingham, Giles E.

2013-01-01

205

Recovery of NMDA receptor currents from MK-801 blockade is accelerated by Mg(2+) and memantine under conditions of agonist exposure.  

PubMed

MK-801 is a use-dependent NMDA receptor open channel blocker with a very slow off-rate. These properties can be exploited to 'pre-block' a population of NMDARs, such as synaptic ones, enabling the selective activation of a different population, such as extrasynaptic NMDARs. However, the usefulness of this approach is dependent on the stability of MK-801 blockade after washout. We have revisited this issue, and confirm that recovery of NMDAR currents from MK-801 blockade is enhanced by channel opening by NMDA, and find that it is further increased when Mg(2+) is also present. In the presence of Mg(2+), 50% recovery from MK-801 blockade is achieved after 10' of 100 ?M NMDA, or 30' of 15 ?M NMDA exposure. In Mg(2+)-free medium, NMDA-induced MK-801 dissociation was found to be much slower. Memantine, another PCP-site antagonist, could substitute for Mg(2+) in accelerating the unblock of MK-801 in the presence of NMDA. This suggests a model whereby, upon dissociation from its binding site in the pore, MK-801 is able to re-bind in a process antagonized by Mg(2+) or another PCP-site antagonist. Finally we show that even when all NMDARs are pre-blocked by MK-801, incubation of neurons with 100 ?M NMDA in the presence of Mg(2+) for 2.5 h triggers sufficient unblocking to kill >80% of neurons. We conclude that while synaptic MK-801 'pre-block' protocols are useful for pharmacologically assessing synaptic vs. extrasynaptic contributions to NMDAR currents, or studying short-term effects, it is problematic to use this technique to attempt to study the effects of long-term selective extrasynaptic NMDAR activation. This article is part of the Special Issue entitled 'Glutamate Receptor-Dependent Synaptic Plasticity'. PMID:23402996

McKay, Sean; Bengtson, C Peter; Bading, Hilmar; Wyllie, David J A; Hardingham, Giles E

2013-02-10

206

Laser acceleration with open waveguides  

SciTech Connect

A unified framework based on solid-state open waveguides is developed to overcome all three major limitations on acceleration distance and hence on the feasibility of two classes of laser acceleration. The three limitations are due to laser diffraction, acceleration phase slippage, and damage of waveguide structure by high power laser. The two classes of laser acceleration are direct-field acceleration and ponderomotive-driven acceleration. Thus the solutions provided here encompass all mainstream approaches for laser acceleration, either in vacuum, gases or plasmas.

Xie, Ming

1999-03-01

207

A proposal for calculating occupational exposure limits for volatile organic compounds acting as sensory irritants on the basis of their physicochemical properties.  

PubMed

A common biological effect of exposure to workplace chemicals is sensory irritation. The ACGIH(R) threshold limit values (TLVs(R)) are developed based on data derived from industrial settings as well as experimental human and animal studies. Considering the limited amount of human data and the tendency to reduce the volume of animal testing, there is a need for an alternative method to assess sensory irritation. Nasal pungency involves transfer of a compound through the mucosa into the receptor area. This environment is inhomogeneous, being partly a hydrophobic lipid-like and hydrophilic aqueous-like area. A general equation has been developed that seems satisfactory for explaining the transfer of volatile organic compounds (VOCs) from the gaseous phase to biophases, making it possible to calculate the nasal pungency threshold (NPT). The obtained correlation between log 1/NPT and log TLV for 71 VOCs, which is based exclusively on their irritant properties, indicates that for the compounds that act through a nonreactive mechanism (alcohols, ketones, esters, ethers, aromatic and aliphatic hydrocarbons, amides) the relationship between these values differs from that calculated for compounds that act through a reactive mechanism (aldehydes, allyl compounds, aliphatic amines, benzyl halides, carboxylic acids, acrylates, and mercaptans). The correlation coefficient for nonreactive VOCs is very high (n = 46, r = 0.89), and it appears that the regression equation (log TLV = -0.422 log 1/NPT + 0.309) could be used to predict occupational exposure limits (OELs) for this group of compounds. Regarding reactive VOCs, the correlation coefficient is considerably lower (n = 25, r = 0.32), which implies that some kind of correction for their reactivity would have to be applied to calculate the OEL values. PMID:20473819

Jakubowski, Marek; Czerczak, S?awomir

2010-07-01

208

Linear Accelerators  

SciTech Connect

In linear accelerators the particles are accelerated by either electrostatic fields or oscillating Radio Frequency (RF) fields. Accordingly the linear accelerators are divided in three large groups: electrostatic, induction and RF accelerators. Overview of the different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of beam focusing in linacs are described.

Sidorin, Anatoly [Joint Institute for Nuclear Research, Joliot-Curie 6, Dubna (Russian Federation)

2010-01-05

209

Examining Geospatial Technology Tools to Compensate for Limited Exposures and Integrate Diverse Map and Data Resources in Geological Studies of the Southern Blue Ridge  

NASA Astrophysics Data System (ADS)

Constraining the tectonic and metamorphic history of rock units in the southern Blue Ridge of western North Carolina is complicated by limited exposures and extensive vegetative cover, as well as burial by human development. Integrating varied data sources for field relations using cyberinformation tools may provide a means around such difficulties. We are examining several different Geographical Information Systems (GIS) tools as a means for effectively integrating available map data, both toward meeting research objectives as well as to facilitate classroom and field instruction. Commercial GIS platforms like ArcGIS and associated software can effectively integrate diverse geoscience information resources within a single platform. The Internet provides free access to databases ranging from geochemical datasets to topographical and structural data. Public domain geochemical databases like EarthChem provide spatially controlled elemental data on rock samples collected by many researchers over extended periods. Once incorporated within the ArcGIS template, this information can then be exported into free geospatial visualization applications such as Goggle Earth, as well as 3D manipulation programs like Fledermaus. Geospatially controlled USGS and NCGS geologic maps and geophysical datasets provide a useful base for examining mafic and ultramafic rock exposures in the Blue Ridge. One can resolve the exposures of specific rock types from these map resources within ArcGIS, as well as fault locations, and magnetics and gravity data. High-resolution DEMs permit data-intensive focusing on areas of interest, and Fledermaus manipulations permit 3D visualization. The output maps and visualizations are of publishable quality, and permit the manipulation of data across a region to infer contact trends and/or chemical or mineralogical, as well as to identify discontinuities that may be geologically relevant. “All-in-one” GIS applications like GeoMapApp have many of these aspects built in, and allow immediate, global-scale representations. However, these systems include relatively limited capabilities for independent data manipulation, and are constrained by the spatial detail of the integrated databases. Absent the ability to separate out individual rock units from geological maps, the regional study of rock associations via GeoMapApp is necessarily problematic. Also, low-resolution topographic base maps and digital elevation models (DEMs) inhibit exports to three-dimensional manipulation programs, and the exported content can only be minimally manipulated. For multivariate geological data resources such as one encounters in the study of mountain belts, an multi-tool approach combining commercial ArcGIS data management with various visualization tools appears to produce the best results in terms of research study of such datasets, and for the production of effective classroom visualizations.

Collins, N.; Ryan, J. G.

2010-12-01

210

Accelerators (3/5)  

ScienceCinema

1a) Introduction and motivation 1b) History and accelerator types 2) Transverse beam dynamics 3a) Longitudinal beam dynamics 3b) Figure of merit of a synchrotron/collider 3c) Beam control 4) Main limiting factors 5) Technical challenges Prerequisite knowledge: Previous knowledge of accelerators is not required.

211

Accelerators (4/5)  

ScienceCinema

1a) Introduction and motivation 1b) History and accelerator types 2) Transverse beam dynamics 3a) Longitudinal beam dynamics 3b) Figure of merit of a synchrotron/collider 3c) Beam control 4) Main limiting factors 5) Technical challenges Prerequisite knowledge: Previous knowledge of accelerators is not required.

212

Accelerators (5/5)  

ScienceCinema

1a) Introduction and motivation 1b) History and accelerator types 2) Transverse beam dynamics 3a) Longitudinal beam dynamics 3b) Figure of merit of a synchrotron/collider 3c) Beam control 4) Main limiting factors 5) Technical challenges Prerequisite knowledge: Previous knowledge of accelerators is not required.

213

Linear Accelerators  

SciTech Connect

In the linear accelerators the particles are accelerated by either electrostatic fields or oscillating radio frequency (RF) fields. Accordingly the linear accelerators are divided by three large groups: electrostatic, induction and RF accelerators. Overview of different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of the beam focusing in linacs are described.

Sidorin, A. [Joint Institute for Nuclear Research, Dubna (Russian Federation)

2007-11-26

214

Administration of Diethylnitrosamine in the Immediate Postnatal Period Coupled with Exposure to a Choline Deficient Diet Accelerates Hepatocarcinogenesis in the Rat  

Microsoft Academic Search

The objectives of this study were to determine if the combination of: i. neonatal administration of diethylnitrosamine and ii. subsequent feeding of a choline deficient diet could accelerate hepatic premalignancy in the rat. The presence and size of premalignant nodules and the activity of the liver cancer enzyme marker g-glutamyltranspeptidase (gGT) were used as indicators of hepatic premalignancy. Three day

Susan Hemmings; Judee Strickland

2002-01-01

215

Plasma accelerators  

SciTech Connect

In this paper we discuss plasma accelerators which might provide high gradient accelerating fields suitable for TeV linear colliders. In particular we discuss two types of plasma accelerators which have been proposed, the Plasma Beat Wave Accelerator and the Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. Finally, we show for the Plasma Wake Field Accelerator that one can accelerate high quality low emittance beams and, in principle, obtain efficiencies and energy spreads comparable to those obtained with conventional techniques.

Ruth, R.D.; Chen, P.

1986-03-01

216

Limiter study  

SciTech Connect

Studies of energy deposition on a mushroom-shaped limiter have been performed on ZT-40M. Total energy deposition, estimated power deposition per unit area, the effects of gas puffing and vertical and error field application, and approximate time histories of the extent of the impact area are presented for two different current levels (120 and 190 kA), protrusions into the body of the plasma (+2 - +12 mm from the wall) and limiter materials. Photographs of a bare graphite and TiC-coated graphite limiter before and after exposure to the plasma are shown. Massive spallation of the TiC-coated limiter is observed at the higher current level. Spallation occurs during the discharge and after termination. The degree of spallation is dependent on the current level. The average power deposition on the limiter over the discharge is estimated to be less than or equal to 1 MW.

Downing, J.N.; Gordon, R.A.; Thomas, K.S.; Watt, R.G.

1983-08-01

217

Effects of limited exposure of rabbit chondrocyte cultures to parathyroid hormone and dibutyryl adenosine 3',5'-monophosphate on cartilage-characteristic proteoglycan synthesis  

SciTech Connect

Treatment of rabbit chondrocyte cultures with PTH or (Bu)2cAMP for 30 h increased by 2- to 3-fold the incorporation of (35S)sulfate and 3H radioactivity with glucosamine as the precursor into large chondroitin sulfate proteoglycans characteristically found in cartilage matrix. However, PTH and (Bu)2cAMP did not increase either (35S)sulfate incorporation into small proteoglycans or the incorporation of 3H radioactivity into hyaluronic acid and other glycosaminoglycans. PTH and (Bu)2cAMP also increased the incorporation of (3H) serine into both proteoglycans and total protein. In all cultures described above, the stimulation of (3H)serine incorporation into proteoglycans exceeded that of (3H)serine incorporation into total protein. These data indicate that PTH and (Bu)2cAMP selectively stimulate cartilage proteoglycan synthesis while they increase total protein synthesis. Since cAMP seems to play a mediatory role in the action of PTH, we elected to examine the effects of a limited exposure of chondrocytes to PTH or (Bu)2cAMP on the synthesis of proteoglycans. Treatment with PTH or (Bu)2cAMP for only the initial 2-7 h did not increase the rates of incorporation of (35S)sulfate, the 3H radioactivity with glucosamine, and (3H)serine into proteoglycans, as measured at 30 h, despite the fact that this treatment brought about a rapid and transient rise in the cAMP level. Furthermore, the application of prostaglandin I2 at concentrations that increased cAMP levels in a similar fashion as did PTH did not affect (35S) sulfate incorporation into proteoglycans.

Kato, Y.; Koike, T.; Iwamoto, M.; Kinoshita, M.; Sato, K.; Hiraki, Y.; Suzuki, F.

1988-05-01

218

FFAGS FOR MUON ACCELERATION.  

SciTech Connect

Due to their finite lifetime, muons must be accelerated very rapidly. It is challenging to make the magnets ramp fast enough to accelerate in a synchrotron, and accelerating in a linac is very expensive. One can use a recirculating accelerator (like CEBAF), but one needs a different arc for each turn, and this limits the number of turns one can use to accelerate, and therefore requires significant amounts of RF to achieve the desired energy gain. An alternative method for muon acceleration is using a fixed field alternating gradient (FFAG) accelerator. Such an accelerator has a very large energy acceptance (a factor of two or three), allowing one to use the same arc with a magnetic field that is constant over time. Thus, one can in principle make as many turns as one can tolerate due to muon decay, therefore reducing the RF cost without increasing the arc cost. This paper reviews the current status of research into the design of FFAGs for muon acceleration. Several current designs are described and compared. General design considerations are also discussed.

BERG,J.S.KAHN,S.PALMER,R.TRBOJEVIC,D.JOHNSTONE,C.KEIL,Y.OGITSU,T.OHMORI,C.SESSLER,A.KOSCIELNIAK,S.

2003-06-26

219

Future accelerators (?)  

SciTech Connect

I describe the future accelerator facilities that are currently foreseen for electroweak scale physics, neutrino physics, and nuclear structure. I will explore the physics justification for these machines, and suggest how the case for future accelerators can be made.

John Womersley

2003-08-21

220

Vibration safety limits for magnetic resonance elastography  

NASA Astrophysics Data System (ADS)

Magnetic resonance elastography (MRE) has been demonstrated to have potential as a clinical tool for assessing the stiffness of tissue in vivo. An essential step in MRE is the generation of acoustic mechanical waves within a tissue via a coupled mechanical driver. Motivated by an increasing volume of human imaging trials using MRE, the objectives of this study were to audit the vibration amplitude of exposure for our IRB-approved human MRE studies, to compare these values to a conservative regulatory standard for vibrational exposure and to evaluate the applicability and implications of this standard for MRE. MRE displacement data were examined from 29 MRE exams, including the liver, brain, kidney, breast and skeletal muscle. Vibrational acceleration limits from a European Union directive limiting occupational exposure to whole-body and extremity vibrations (EU 2002/44/EC) were adjusted for time and frequency of exposure, converted to maximum displacement values and compared to the measured in vivo displacements. The results indicate that the vibrational amplitudes used in MRE studies are below the EU whole-body vibration limit, and the EU guidelines represent a useful standard that could be readily accepted by Institutional Review Boards to define standards for vibrational exposures for MRE studies in humans.

Ehman, E. C.; Rossman, P. J.; Kruse, S. A.; Sahakian, A. V.; Glaser, K. J.

2008-02-01

221

Limitations of the American Society of Therapeutic Radiology and Oncology Consensus Panel Guidelines on the Use of Accelerated Partial Breast Irradiation  

SciTech Connect

Purpose: We applied the American Society of Therapeutic Radiology and Oncology (ASTRO) Consensus Panel (CP) guidelines for the use of accelerated partial breast irradiation (APBI) to patients treated with this technique to determine the ability of the guidelines to differentiate patients with significantly different clinical outcomes. Methods and Materials: A total of 199 patients treated with APBI and 199 with whole-breast irradiation (WBI) (matched for tumor size, nodal status, age, margins, receptor status, and tamoxifen use) were stratified into the three ASTRO CP levels of suitability ('suitable,' 'cautionary,' and 'unsuitable') to assess rates of ipsilateral breast tumor recurrence (IBTR), regional nodal failure, distant metastases, disease-free survival, cause-specific survival, and overall survival based on CP category. Median follow-up was 11.1 years. Results: Analysis of the APBI and WBI patient groups, either separately or together (n = 398), did not demonstrate statistically significant differences in 10-year actuarial rates of IBTR when stratified by the three ASTRO groups. Regional nodal failure and distant metastasis were generally progressively worse when comparing the suitable to cautionary to unsuitable CP groups. However, when analyzing multiple clinical, pathologic, or treatment-related variables, only patient age was associated with IBTR using WBI (p = 0.002). Conclusions: The ASTRO CP suitable group predicted for a low risk of IBTR; however, the cautionary and unsuitable groups had an equally low risk of IBTR, supporting the need for continued refinement of patient selection criteria as additional outcome data become available and for the continued accrual of patients to Phase III trials.

Vicini, Frank, E-mail: fvicini@beaumont.ed [Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI (United States); Arthur, Douglas [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA (United States); Wazer, David [Department of Radiation Oncology, Tufts University School of Medicine, Boston, MA (United States); Chen, Peter; Mitchell, Christina; Wallace, Michelle; Kestin, Larry; Ye, Hong [Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI (United States)

2011-03-15

222

Accelerator search for cosmic SIMPs  

Microsoft Academic Search

We give limits on the contribution to the cosmic dark matter density of neutral, stable, strongly interacting massive particles (SIMPs). The limits are inferred from an accelerator mass spectrometry (AMS) experiment at the Purdue Rare Isotope Measurement Laboratory (PRIME Lab). The experiment accelerated nuclei of both gold and iron. The “SIMP signal” would be discovery of nuclei of these elements

V. Teplitz; D. Javorsek; E. Fischbach; R. Mohapatra

2003-01-01

223

The role of reported tobacco-specific media exposure on adult attitudes towards proposed policies to limit the portrayal of smoking in movies  

PubMed Central

Objective To assess the relative, independent contribution of reported tobacco-specific media exposure (pro-tobacco advertising, anti-tobacco advertising, and news coverage of tobacco issues) to US adults’ support for policy efforts that aim to regulate the portrayal of smoking in movies. Methods Using the American Legacy Foundation’s 2003 American Smoking and Health Survey (ASHES-2), multivariable logistic regression was used to model the predicted probability that US adults support movie-specific tobacco control policies, by reported exposure to tobacco-specific media messages, controlling for smoking status, education, income, race/ethnicity, age, sex, knowledge of the negative effects of tobacco and state. Results Across most outcome variables under study, findings reveal that reported exposure to tobacco-specific media messages is associated with adult attitudes towards movie-specific policy measures. Most exposure to tobacco information in the media (with the exception of pro-tobacco advertising on the internet) contributes independently to the prediction of adult support for movie-specific policies. The direction of effect follows an expected pattern, with reported exposure to anti-tobacco advertising and news coverage of tobacco predicting supportive attitudes towards movie policies, and reported exposure to pro-tobacco advertising lessening support for some movie policies, though the medium of delivery makes a difference. Conclusion Media campaigns to prevent tobacco use and exposure to secondhand smoke have had value beyond the intended impact of single-issue campaigns; exposure to anti-tobacco campaigns and public dialogue about the dangers of tobacco seem also to be associated with shaping perceptions of the social world related to norms about tobacco, and ideas about regulating the portrayal of smoking in movies.

Blake, Kelly D; Viswanath, K; Blendon, Robert J; Vallone, Donna

2011-01-01

224

Ion Induction Accelerators  

NASA Astrophysics Data System (ADS)

The description of beams in RF and induction accelerators share many common features. Likewise, there is considerable commonality between electron induction accelerators (see Chap. 7) and ion induction accelerators. However, in contrast to electron induction accelerators, there are fewer ion induction accelerators that have been operated as application-driven user facilities. Ion induction accelerators are envisioned for applications (see Chap. 10) such as Heavy Ion Fusion (HIF), High Energy Density Physics (HEDP), and spallation neutron sources. Most ion induction accelerators constructed to date have been limited scale facilities built for feasibility studies for HIF and HEDP where a large numbers of ions are required on target in short pulses. Because ions are typically non-relativistic or weakly relativistic in much of the machine, space-charge effects can be of crucial importance. This contrasts the situation with electron machines, which are usually strongly relativistic leading to weaker transverse space-charge effects and simplified longitudinal dynamics. Similarly, the bunch structure of ion induction accelerators relative to RF machines results in significant differences in the longitudinal physics.

Barnard, John J.; Horioka, Kazuhiko

225

Accelerated atmospheric corrosion testing using a cyclic wet/dry exposure test; Galvanic couples of aluminum with graphite neoprene rubber, galvanized steel, and steel  

SciTech Connect

Aluminum corrosion is important in overhead electrical conductors constructed from aluminum wire centrally reinforced by galvanized steel strands. Inspection of conductor after long service has implicated rubber bushing material, on the outside, and the galvanized strands, on the inside, as providing potential galvanic sites for the initiation of rapid aluminum corrosion. Therefore, the galvanic corrosion of aluminum in contact with graphite-loaded neoprene rubber, hot-dip galvanized steel and steel was assessed in a cyclic wet/dry exposure test using mixed-salts spray solutions containing appropriate ratios of sulfate and chloride ion. Aluminum was found to corrode at between 3 to 6 times its uncoupled rate when associated with the rubber material. While the eta-phase, relatively pure Zn, galvanized layer remained intact, galvanic corrosion of aluminum was slow. However, on exposure of the zeta-phase, Zn/Fe intermetallic layer, aluminum corroded about 35 times faster than expected in a solution with a high level of Cl{sup -} ion. The importance of these data to conductor lifetime is discussed.

Lyon, S.B.; Thompson, G.E.; Johnson, J.E.; Wood, G.C. (Manchester Univ. (UK). Inst. of Science and Technology); Ferguson, J.M. (Central Electricity Generating Board, Guildford (UK))

1989-11-01

226

New accelerated weathering tests including acid rain  

Microsoft Academic Search

Aprocedure for the design of reliable accelerated weathering tests for service life prediction of automotive coatings was\\u000a developed and used in designing an accelerated test based on SAE method J 1960. The influence of exposure conditions was investigated\\u000a in several accelerated tests. Results from these tests and from Florida exposures were used to optimize test conditions. A\\u000a test cycle that

Magnus Palm; Bo Carlsson

2002-01-01

227

LONG DAY PHOTOPERIOD THAT ENHANCES PUBERTY DOES NOT LIMIT BODY GROWTH IN HOLSTEIN HEIFERS.  

Technology Transfer Automated Retrieval System (TEKTRAN)

As extended photoperiod accelerates puberty, it may limit mature body size and be detrimental to ultimate milk yield during lactation. We hypothesized that the potential negative effects of rapid growth and puberty through long day photoperiod (LDPP) exposure could be overcome with a greater supply ...

228

Ultra Accelerated Testing of PV Module Components  

SciTech Connect

Using concentrated natural sunlight at the NREL High Flux Solar Furnace, we have exposed several materials to acceleration factors of up to 400 times the normal outdoor UV exposure dose. This accelerated rate allows the exposure of materials such that a year of outdoor exposure can be simulated in about 5 hours. We have studied the solarization of cerium containing glass, the degradation of ethylene vinyl acetate laminated between borosilicate glass, and the yellowing of standard polystyrene test coupons. The first two candidates are of interest to the photovoltaics (PV) program, and the last candidate material is a widely used dosimeter for ultra violet (UV) exposure in accelerated weathering chambers

Pitts, J. R.; King, D. E.; Bingham, C.; Czanderna, A. W.

1998-10-28

229

Prenatal exposure to escitalopram and/or stress in rats produces limited effects on endocrine, behavioral, or gene expression measures in adult male rats.  

PubMed

Stress and/or antidepressants during pregnancy have been implicated in a wide range of long-term effects in the offspring. We investigated the long-term effects of prenatal stress and/or clinically relevant antidepressant exposure on male adult offspring in a model of the pharmacotherapy of maternal depression. Female Sprague-Dawley rats were implanted with osmotic minipumps that delivered clinically relevant exposure to the antidepressant escitalopram throughout gestation. Subsequently, pregnant females were exposed on gestational days 10-20 to a chronic unpredictable mild stress paradigm. The male offspring were analyzed in adulthood. Baseline physiological measurements were largely unaltered by prenatal manipulations. Behavioral characterization of the male offspring, with or without pre-exposure to an acute stressor, did not reveal any group differences. Prenatal stress exposure resulted in a faster return towards baseline following the peak response to an acute restraint stressor, but not an airpuff startle stressor, in adulthood. Microarray analysis of the hippocampus and hypothalamus comparing all treatment groups revealed no significantly-altered transcripts. Real time PCR of the hippocampus confirmed that several transcripts in the CRFergic, serotonergic, and neural plasticity pathways were unaffected by prenatal exposures. This stress model of maternal depression and its treatment indicate that escitalopram use and/or stress during pregnancy produced no alterations in our measures of male adult behavior or the transcriptome, however prenatal stress exposure resulted in some evidence for increased glucocorticoid negative feedback following an acute restraint stress. Study design should be carefully considered before implications for human health are ascribed to prenatal exposure to stress or antidepressant medication. PMID:23906943

Bourke, Chase H; Stowe, Zachary N; Neigh, Gretchen N; Olson, Darin E; Owens, Michael J

2013-07-30

230

Phase II Study of Accelerated High-Dose Radiotherapy With Concurrent Chemotherapy for Patients With Limited Small-Cell Lung Cancer: Radiation Therapy Oncology Group Protocol 0239  

SciTech Connect

Purpose: To investigate whether high-dose thoracic radiation given twice daily during cisplatin-etoposide chemotherapy for limited small-cell lung cancer (LSCLC) improves survival, acute esophagitis, and local control rates relative to findings from Intergroup trial 0096 (47%, 27%, and 64%). Patients and Methods: Patients were accrued over a 3-year period from 22 US and Canadian institutions. Patients with LSCLC and good performance status were given thoracic radiation to 61.2 Gy over 5 weeks (daily 1.8-Gy fractions on days 1-22, then twice-daily 1.8-Gy fractions on days 23-33). Cisplatin (60 mg/m{sup 2} IV) was given on day 1 and etoposide (120 mg/m{sup 2} IV) on days 1-3 and days 22-24, followed by 2 cycles of cisplatin plus etoposide alone. Patients who achieved complete response were offered prophylactic cranial irradiation. Endpoints included overall and progression-free survival; severe esophagitis (Common Toxicity Criteria v 2.0) and treatment-related fatalities; response (Response Evaluation Criteria in Solid Tumors); and local control. Results: Seventy-two patients were accrued from June 2003 through May 2006; 71 were evaluable (median age 63 years; 52% female; 58% Zubrod 0). Median survival time was 19 months; at 2 years, the overall survival rate was 36.6% (95% confidence interval [CI] 25.6%-47.7%), and progression-free survival 19.7% (95% CI 11.4%-29.6%). Thirteen patients (18%) experienced severe acute esophagitis, and 2 (3%) died of treatment-related causes; 41% achieved complete response, 39% partial response, 10% stable disease, and 6% progressive disease. The local control rate was 73%. Forty-three patients (61%) received prophylactic cranial irradiation. Conclusions: The overall survival rate did not reach the projected goal; however, rates of esophagitis were lower, and local control higher, than projected. This treatment strategy is now one of three arms of a prospective trial of chemoradiation for LSCLC (Radiation Therapy Oncology Group 0538/Cancer and Leukemia Group B 30610).

Komaki, Ritsuko, E-mail: rkomaki@mdanderson.org [Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas (United States); Paulus, Rebecca [Radiation Therapy Oncology Group Statistical Center, Philadelphia, Pennsylvania (United States); Ettinger, David S. [Department of Oncology, Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland (United States); Videtic, Gregory M.M. [Department of Radiation Oncology, Cleveland Clinic, Cleveland, Ohio (United States); Bradley, Jeffrey D. [Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri (United States); Glisson, Bonnie S. [Department of Thoracic/Head and Neck Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas (United States); Langer, Corey J. [Thoracic Oncology, Abramson Cancer Center, University of Pennsylvania, Philadelphia, Pennsylvania (United States); Sause, William T. [Radiation Center, LDS Hospital, Salt Lake City, Utah (United States); Curran, Walter J. [Department of Radiation Oncology, Jefferson Medical College, Philadelphia, Pennsylvania (United States); Choy, Hak [Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas (United States)

2012-07-15

231

Accelerated Testing of Epoxy-FRP Composites for Civil Infrastructure Applications: Property Changes and Mechanisms of Degradation  

Microsoft Academic Search

Accelerated testing of FRP systems is frequently performed due to the long service life of these materials used to repair damaged civil structures. This testing typically involves exposure to common environmental conditions seen in the field. However, the main limitation of these experiments is that the testing protocols typically do not consider a change in the failure mechanism as a

Andrew Stewart; Elliot P. Douglas

2012-01-01

232

The Influence of an Air Exposure on the Secondary Electron Yield of Copper  

Microsoft Academic Search

Abstract The influence of different air exposure times on the secondary electron emission of clean copper surfaces as well as on technical copper surfaces has been studied in the context of the phenomenon of multipacting, which can limit the performance of superconducting radio-frequency (RF) cavities for particle acceleration. The copper samples were prepared by heat treatments and in situ sputter-etching

C Scheuerlein; Noël Hilleret

1997-01-01

233

Accelerated Reader.  

ERIC Educational Resources Information Center

|This paper provides an overview of Accelerated Reader, a system of computerized testing and record-keeping that supplements the regular classroom reading program. Accelerated Reader's primary goal is to increase literature-based reading practice. The program offers a computer-aided reading comprehension and management program intended to motivate…

Education Commission of the States, Denver, CO.

234

Radical Acceleration  

ERIC Educational Resources Information Center

|Research has found that teachers' objections to accelerating gifted students are mainly based on a fear that acceleration will lead to social or emotional damage. Ironically, it is the academic and emotional maturity which characterizes intellectually gifted students, coupled with their high levels of academic achievement, which makes them such…

Gross, Miraca U. M.; Van Vliet, Helen E.

2005-01-01

235

Research paper Limited ice-sheet erosion and complex exposure histories derived from in situ cosmogenic 10Be, 26Al, and 14C on Baffin Island, Arctic Canada  

Microsoft Academic Search

Discordant cosmogenic nuclide exposure ages derived from 10Be, 26Al, and 14C extracted from quartz in rocky summits along the eastern rim of the central Baffin Island plateau provide constraints on the efficiency of erosion by the Laurentide Ice Sheet (LIS) and on the timing and duration of ice-free conditions in the eastern Canadian Arctic. In situ 14C records the duration

Gifford H. Miller; Jason P. Briner; Nathaniel A. Lifton; Robert C. Finkel

236

Limited ice-sheet erosion and complex exposure histories derived from in situ cosmogenic 10Be, 26Al, and 14C on Baffin Island, Arctic Canada  

Microsoft Academic Search

Discordant cosmogenic nuclide exposure ages derived from 10Be, 26Al, and 14C extracted from quartz in rocky summits along the eastern rim of the central Baffin Island plateau provide constraints on the efficiency of erosion by the Laurentide Ice Sheet (LIS) and on the timing and duration of ice-free conditions in the eastern Canadian Arctic. In situ 14C records the duration

Gifford H. Miller; Jason P. Briner; Nathaniel A. Lifton; Robert C. Finkel

2006-01-01

237

The role of reported tobacco-specific media exposure on adult attitudes towards proposed policies to limit the portrayal of smoking in movies  

Microsoft Academic Search

ObjectiveTo assess the relative, independent contribution of reported tobacco-specific media exposure (pro-tobacco advertising, anti-tobacco advertising, and news coverage of tobacco issues) to US adults' support for policy efforts that aim to regulate the portrayal of smoking in movies.MethodsUsing the American Legacy Foundation's 2003 American Smoking and Health Survey (ASHES-2), multivariable logistic regression was used to model the predicted probability that

Kelly D Blake; K. Viswanath; Robert J Blendon; Donna Vallone

2010-01-01

238

Plasma based accelerators  

NASA Astrophysics Data System (ADS)

A plasma medium can support a variety of wave motions which may be useful for accelerating charged particles. For highly relativistic beams the longitudinal electrostatic wave is most suitable and may be driven by laser or by particle beams. The basic principles, limitations and prospects for these devices are discussed.

Evans, R. G.

1987-05-01

239

COLLECTIVE PHENOMENA IN ACCELERATORS  

Microsoft Academic Search

Recent years have witnessed the development of accelerators of ever-larger current, both peak and average, as well as a proliferation of storage rings of ever-greater luminosity. Consequently, there is considerable interest in and growing concern with, the phenomena which limit beam currents and beam densities, namely, the collective modes of behavior of relativistic particle beams. Furthermore, it has been demonstrated

Sessler; Andrew M

1972-01-01

240

Wakefield accelerators  

SciTech Connect

The search for new methods to accelerate particle beams to high energy using high gradients has resulted in a number of candidate schemes. One of these, wakefield acceleration, has been the subject of considerable R D in recent years. This effort has resulted in successful proof of principle experiments and in increased understanding of many of the practical aspects of the technique. Some wakefield basics plus the status of existing and proposed experimental work is discussed, along with speculations on the future of wake field acceleration. 10 refs., 6 figs.

Simpson, J.D.

1990-01-01

241

Acceleration Tolerance After Ingestion of a Commercial Energy Drink.  

National Technical Information Service (NTIS)

This study examined the ability of a commercial energy drink to enhance acceleration tolerance, strength under G-load, and cognitive performance immediately prior to and following acceleration exposure. Eight experienced centrifuge subjects completed thre...

G. L. Warren J. Fischer T. B. Walker U. Balldin W. Storm

2010-01-01

242

Podcast: Acceleration  

NSDL National Science Digital Library

The Podcast: Acceleration is a segment of the Force and Motion Short Course. The podcast is 2 minutes 13 seconds in duration. Presented by science experts and NSTA staff, the NSTA Online Short Courses are professional development opportunities de

2009-07-06

243

Acceleration switch  

DOEpatents

The disclosure relates to an improved integrating acceleration switch of the type having a mass suspended within a fluid filled chamber, with the motion of the mass initially opposed by a spring and subsequently not so opposed.

Abbin, Jr., Joseph P. (Albuquerque, NM); Devaney, Howard F. (Cedar Crest, NM); Hake, Lewis W. (Albuquerque, NM)

1982-08-17

244

Angular Acceleration  

NSDL National Science Digital Library

The simulation of a rotating wheel below shows the relationship between angular position, angular velocity, and angular acceleration. Graphs of angular position and angular velocity as a function of time are shown.

Christian, Wolfgang; Belloni, Mario

2008-02-19

245

ION ACCELERATOR  

DOEpatents

An arrangement for the drift tubes in a linear accelerator is described whereby each drift tube acts to shield the particles from the influence of the accelerating field and focuses the particles passing through the tube. In one embodiment the drift tube is splii longitudinally into quadrants supported along the axis of the accelerator by webs from a yoke, the quadrants. webs, and yoke being of magnetic material. A magnetic focusing action is produced by energizing a winding on each web to set up a magnetic field between adjacent quadrants. In the other embodiment the quadrants are electrically insulated from each other and have opposite polarity voltages on adjacent quadrants to provide an electric focusing fleld for the particles, with the quadrants spaced sufficienily close enough to shield the particles within the tube from the accelerating electric field.

Bell, J.S.

1959-09-15

246

Accelerated molecular dynamics methods  

SciTech Connect

The molecular dynamics method, although extremely powerful for materials simulations, is limited to times scales of roughly one microsecond or less. On longer time scales, dynamical evolution typically consists of infrequent events, which are usually activated processes. This course is focused on understanding infrequent-event dynamics, on methods for characterizing infrequent-event mechanisms and rate constants, and on methods for simulating long time scales in infrequent-event systems, emphasizing the recently developed accelerated molecular dynamics methods (hyperdynamics, parallel replica dynamics, and temperature accelerated dynamics). Some familiarity with basic statistical mechanics and molecular dynamics methods will be assumed.

Perez, Danny [Los Alamos National Laboratory

2011-01-04

247

Design and estimation of coded exposure point spread functions.  

PubMed

We address the problem of motion deblurring using coded exposure. This approach allows for accurate estimation of a sharp latent image via well-posed deconvolution and avoids lost image content that cannot be recovered from images acquired with a traditional shutter. Previous work in this area has used either manual user input or alpha matting approaches to estimate the coded exposure Point Spread Function (PSF) from the captured image. In order to automate deblurring and to avoid the limitations of matting approaches, we propose a Fourier-domain statistical approach to coded exposure PSF estimation that allows us to estimate the latent image in cases of constant velocity, constant acceleration, and harmonic motion. We further demonstrate that previously used criteria to choose a coded exposure PSF do not produce one with optimal reconstruction error, and that an additional 30 percent reduction in Root Mean Squared Error (RMSE) of the latent image estimate can be achieved by incorporating natural image statistics. PMID:22585096

McCloskey, Scott; Ding, Yuanyuan; Yu, Jingyi

2012-10-01

248

Psychological Effects of Thought Acceleration  

Microsoft Academic Search

Six experiments found that manipulations that increase thought speed also yield positive affect. These experiments varied in both the methods used for accelerating thought (i.e., instructions to brainstorm freely, exposure to multiple ideas, encouragement to plagiarize others' ideas, performance of easy cognitive tasks, narration of a silent video in fast-forward, and experimentally controlled reading speed) and the contents of the

Emily Pronin; Elana Jacobs; Daniel M. Wegner

2008-01-01

249

Damage characterization of SiN x-ray mask membrane caused by electron-beam exposure  

Microsoft Academic Search

The effects of exposure damage with an electron beam of 20 to 50 kV acceleration voltage on silicon nitride film prepared by LPCVD system have been investigated. It is shown that the optical and mechanical properties of this material are modified and may potentially limit the use as a membrane in an x-ray mask structure for the high density memory

Sang-Soo Choi; Young-Beom D. Jeon; Jong-Soo Kim; Hai Bin Chung; Sang-Yun Lee; Jong-Hyun Lee; Hyung-Joun Yoo

1996-01-01

250

Radiation limits  

SciTech Connect

Recently several changes were made to the regulations governing the limits of allowable exposure to radiation for industrial radiographers and nuclear power plant workers. Even though these regulations effect people who have been trained and educated about radiation`s dangers, changes still bring up many common questions that may not be readily answered by the regulations themselves. This paper will attempt to answer some of the more common and relevant questions that are being asked in industry. Who is involved in setting the regulations and standards? (Who are ``They?``) What are the differences between the old and the new regulations? Why did the regulations change? How do ``They`` know what is safe? Have these standards been changed before? Will there be future changes?

Hassard, M. [Salt Lake Community Coll., Salt Lake City, UT (United States)

1997-09-01

251

Accelerated Degradation of Polymers  

NSDL National Science Digital Library

For this laboratory exercise, you will monitor changes in the visual appearance of the samples, chemical changes and molecular weight changes as a function of exposure condition. Analysis of the neat and degraded systems will be done using visual evaluation, FTIR analysis and GPC analysis. After in-class presentation, completion of hands-on laboratory experiment and review of the information provided, you should be able to: ⢠Confidently discuss the mechanism of breakdown for a polymeric material exposed to various environmental conditions. ⢠Prepare samples and record an accurate account of their preparation for use in an outdoor environment and in an accelerated weathering chamber (Q-sun).

Derosa, Rebecca L.

2008-09-26

252

Pre-Exposure Antiretroviral Prophylaxis (PrEP) attitudes in high risk Boston area MSM: Limited knowledge and experience, but potential for increased utilization after education  

PubMed Central

Background Pre-exposure prophylaxis (PrEP) could protect individuals engaging in repeated high-risk behaviors from HIV infection. Understanding the demographic and behavioral predictors of intent to use PrEP may prove useful to identify clinical trial participants. Methods In 2007, 227 HIV-uninfected MSM recruited through modified respondent-driven sampling completed an interviewer-administered survey assessing prior PrEP use and awareness, future intent to use PrEP, demographics, sexual risk, psychosocial variables, and drug/alcohol use. Bivariate and multivariable logistic regression procedures examined predictors of intention to use PrEP. Results Mean age of participants was 41 (SD=9.1); 54% were non-white. One participant reported prior off-label PrEP use (medication obtained from his HIV-infected brother). Nineteen percent had previously heard of PrEP, while 74% reported intent to use PrEP if available after being educated about its potential. In multivariable analysis controlling for age and race/ethnicity, significant predictors of intent to use PrEP included: less education (OR=7.7; p=0.04), moderate income (OR=13.0; p=0.04), no perceived side effects from taking PrEP (OR=3.5; p=0.001), and not having to pay for PrEP (OR=4.2; p=0.05). Discussion Many New England MSM indicated an interest in using PrEP after learning about its potential, particularly if they could obtain PrEP at no expense and if PrEP had no side effects. Less educated MSM and those who knew less about PrEP and antiretroviral therapy (ART) before entering the study were more open to using ART for prevention once they had received some information suggesting its potential value. Findings suggest careful educational messages are necessary to ensure appropriate PrEP use if clinical trials reveal partial efficacy.

Mimiaga, Matthew J.; Case, Patricia; Johnson, Carey V.; Safren, Steven A.; Mayer, Kenneth H.

2009-01-01

253

Repeated exposure to 5D9, an inhibitor of 3D polymerase, effectively limits the replication of foot-and-mouth disease virus in host cells.  

PubMed

Foot-and-mouth disease (FMD) is a highly contagious disease of livestock caused by a highly variable RNA virus (FMDV) that has seven serotypes and more than sixty subtypes. Both prophylactic and post-infection means of controlling the disease outbreak, including universally applicable vaccines and emergency response measures such as therapeutic treatments, are on high demand. In this study, we analyzed the long-term exposure outcome to a previously identified inhibitor of 3D polymerase (FMDV 3Dpol) for controlling FMDV infection and for the selection of resistance mutants. The results showed that no escape mutant viruses were isolated from FMDV A24 Cruzeiro infections in cell culture treated with gradually increasing concentrations of the antiviral compound 5D9 (4-chloro-N'-thieno, [2,3-d]pyrimidin-4-ylbenzenesulfonohydrazide) over ten passages. Biochemical and plaque assays revealed that when 5D9 was used at concentrations within a non-toxic range in cells, it drove the virus to undetectable levels at passage eight to ten. This is in contrast with observations made on parallel control (untreated) passages exhibiting fully viable and stable virus progenies. Collectively, the results demonstrated that under the experimental conditions, treatment with 5D9 does not confer a resistant phenotype and the virus is unable to evade the antiviral effect of the inhibitor. Further efforts using quantitative structure-property relationship (QSPR) based modifications of the 5D9 compound may result in the successful development of an effective in vivo antiviral drug targeting FMDV. PMID:23578728

Rai, Devendra K; Schafer, Elizabeth A; Singh, Kamalendra; McIntosh, Mark A; Sarafianos, Stefan G; Rieder, Elizabeth

2013-04-08

254

Possibilities and limitations of fluorescence in situ hybridization technique in retrospective detection of low dose radiation exposure in post-chernobyl human cohorts.  

PubMed

Cytogenetic analysis using the fluorescence in situ hybridisation (FISH) technique was performed late time after the Chernobyl accident in groups of liquidators, evacuees from 30 km exclusive zone, residents of radioactively contaminated areas and control donors age-matched to exposed persons. Stable and unstable chromosome type exchanges were recorded using a hybrid conventional-PAINT nomenclature. The mean yield of stable chromosome exchanges in liquidators did not correlate with registered radiation doses but had a clear negative dependence on the duration of liquidators' staying in Chernobyl zone, that was in a good agreement with early data based on conventional dicentrics plus rings analysis. The overspontaneous excess for stable chromosome exchange level appeared to be higher in evacuees 16-40 years old than that of senior persons, whereas no age-dependent difference occurred for initially induced dicentrics plus rings yields in this cohort. The stable chromosome exchange yield, as well as combined yield of dicentrics plus rings and potentially unstable incomplete translocations in residents of radioactively contaminated areas showed a reasonable positive correlation with levels of 137Cs contamination. The observed yields of stable chromosome exchanges in all three exposed groups appeared to be somewhat lower than those of expected from unstable exchange-based doses which were referred to an in vitro dose response of stable exchanges outcome in human lymphocytes. Thus, FISH analysis can be successfully applied for qualitative cytogenetic indication of past and chronic radiation exposure to low doses but further refinement of FISH-based system for quantitative dose assessment is still required. Some practical approaches of solving this task are discussed. PMID:16396328

Maznyk, N A; Vinnikov, V A

255

Accelerated degradation studies of MEH-PPV  

SciTech Connect

MEH-PPV, which normally has a reddish color, is well known to show photobleaching problems. The photobleaching can be greatly accelerated by exposure to laser light while in air. For example, shining 457 mn light of relatively low intensity (0.06 W/cm{sup 2}) on the MEH-PPV causes the photoluminescence to decrease by a factor of two within a few seconds of exposure, and to show a nearly complete bleaching of the material within 30 minutes. The degradation rate is strongly influenced by laser power, sample thickness, oxygen exposure during preparation and spinning, as well as the oxygen environment during the measurement. The photobleach is indicative of one class of degradation mechanisms limiting the usefulness of PPV based polymers in electroluminescent devices. MEH-PPV which was spin coated in a nitrogen environment and measured in vacuum showed no measurable photo-chemical degradation for measuring times of up to several hours. A dramatic decrease in PL intensity was observed, however, in the presence of oxygen, as well as in samples spin coated in air, but measured in vacuum. We present data on the PL of MEH-PPV, as a function of oxygen concentration.

Radousky, H.B.; Madden, A.D.; Pakbaz, K.; Hagler, T.W.; Lee, H.W.H.; Lorenzana, H.E.; Fox, G.A.; Elliker, P.R.

1995-07-01

256

The Financial Labor Supply Accelerator  

Microsoft Academic Search

When minimum equity stakes in durable goods constrain a household's debt, a persistent wage increase generates a liquidity shortage. This tem- porarily limits the income effect, so hours worked grow. This is the finan- cial labor supply accelerator, which links labor supply decisions to limits on household borrowing. This paper examines its implications for the comove- ment of hours worked

Jeffrey R. Campbell; Zvi Hercowitz

2009-01-01

257

MUON ACCELERATION  

SciTech Connect

One of the major motivations driving recent interest in FFAGs is their use for the cost-effective acceleration of muons. This paper summarizes the progress in this area that was achieved leading up to and at the FFAG workshop at KEK from July 7-12, 2003. Much of the relevant background and references are also given here, to give a context to the progress we have made.

BERG,S.J.

2003-11-18

258

Radiation Safety System for SPIDER Neutral Beam Accelerator  

NASA Astrophysics Data System (ADS)

SPIDER (Source for Production of Ion of Deuterium Extracted from RF Plasma only) and MITICA (Megavolt ITER Injector Concept Advanced) are the ITER neutral beam injector (NBI) testing facilities of the PRIMA (Padova Research Injector Megavolt Accelerated) Center. Both injectors accelerate negative deuterium ions with a maximum energy of 1 MeV for MITICA and 100 keV for SPIDER with a maximum beam current of 40 A for both experiments. The SPIDER facility is classified in Italy as a particle accelerator. At present, the design of the radiation safety system for the facility has been completed and the relevant reports have been presented to the Italian regulatory authorities. Before SPIDER can operate, approval must be obtained from the Italian Regulatory Authority Board (IRAB) following a detailed licensing process. In the present work, the main project information and criteria for the SPIDER injector source are reported together with the analysis of hypothetical accidental situations and safety issues considerations. Neutron and photon nuclear analysis is presented, along with special shielding solutions designed to meet Italian regulatory dose limits. The contribution of activated corrosion products (ACP) to external exposure of workers has also been assessed. Nuclear analysis indicates that the photon contribution to worker external exposure is negligible, and the neutron dose can be considered by far the main radiation protection issue. Our results confirm that the injector has no important radiological impact on the population living around the facility.

Sandri, S.; Coniglio, A.; D'Arienzo, M.; Poggi, C.

2011-12-01

259

Radiation Safety System for SPIDER Neutral Beam Accelerator  

SciTech Connect

SPIDER (Source for Production of Ion of Deuterium Extracted from RF Plasma only) and MITICA (Megavolt ITER Injector Concept Advanced) are the ITER neutral beam injector (NBI) testing facilities of the PRIMA (Padova Research Injector Megavolt Accelerated) Center. Both injectors accelerate negative deuterium ions with a maximum energy of 1 MeV for MITICA and 100 keV for SPIDER with a maximum beam current of 40 A for both experiments. The SPIDER facility is classified in Italy as a particle accelerator. At present, the design of the radiation safety system for the facility has been completed and the relevant reports have been presented to the Italian regulatory authorities. Before SPIDER can operate, approval must be obtained from the Italian Regulatory Authority Board (IRAB) following a detailed licensing process. In the present work, the main project information and criteria for the SPIDER injector source are reported together with the analysis of hypothetical accidental situations and safety issues considerations. Neutron and photon nuclear analysis is presented, along with special shielding solutions designed to meet Italian regulatory dose limits. The contribution of activated corrosion products (ACP) to external exposure of workers has also been assessed. Nuclear analysis indicates that the photon contribution to worker external exposure is negligible, and the neutron dose can be considered by far the main radiation protection issue. Our results confirm that the injector has no important radiological impact on the population living around the facility.

Sandri, S.; Poggi, C. [ENEA, Radiation Protection Institute, IRP-FUAC, Frascati (Italy); Coniglio, A. [Medical Physics Department, S. Giovanni Calibita Hospital, Fatebenefratelli, Isola Tiberina, Roma (Italy); D'Arienzo, M. [ENEA, Ionizing Radiation Metrology National Institute, METR, Casaccia, Rome (Italy)

2011-12-13

260

Cherenkov wakefield accelerators: Rippled waveguides  

SciTech Connect

The properties of using periodically rippled waveguides as wakefield accelerators are investigated. An analysis is performed in the ultrarelativistic limit which accurately predicts the amplitude, wavelength of the wakefield, and their dependences on waveguide and drive beam parameters. These devices are found to have the properties that the synchronous transverse wake vanishes, and the accelerating field is independent of the radial position in the drift tube and independent of the radial profile of the drive beam current. The effects of the nonsynchronous wakefields are discussed. Also, particle-in-cell simulations are performed which agree with the analysis and reveal self-consistent and collective effects in particle acceleration. 20 refs., 2 figs.

Jones, M.E.; Keinigs, R.K.; Peter, W.; Wilks, S.C.

1989-01-01

261

Accelerators and the Accelerator Community  

SciTech Connect

In this paper, standing back--looking from afar--and adopting a historical perspective, the field of accelerator science is examined. How it grew, what are the forces that made it what it is, where it is now, and what it is likely to be in the future are the subjects explored. Clearly, a great deal of personal opinion is invoked in this process.

Malamud, Ernest; Sessler, Andrew

2008-06-01

262

Perspectives of personnel external dosimetry at Stanford Linear Accelerator Center  

Microsoft Academic Search

The need for providing personnel external monitoring for exposure to low- energy photon (< 150 keV) and beta radiation at the Stanford Linear Accelerator Center (SLAC) has been studied. At SLAC, a high energy electron accelerator facility, the major sources of low-energy photons and betas (electron and positron) are from the induced activities in accelerator parts and components. Shower theory

J. C. Liu; D D Busick; K. R. Kase; R. C. McCall; R. Sit; H. Tran

1995-01-01

263

Laser Acceleration in Vacuum and Gases with Capillary Waveguide  

SciTech Connect

A unified framework is developed to overcome all three major limitations on acceleration and distance and hence on the feasibility of two classes of laser acceleration. The three limitations are due to laser diffraction, acceleration phase slippage, and structure damage by high power laser if solid-state optical waveguide is used. The two classes of laser acceleration are direct-field acceleration and ponderomotive-driven acceleration. Thus this letter and its companion [1] provide solutions that are crucial to all mainstream approaches for laser acceleration, either in vacuum, gases or plasmas.

Xie, Ming

1999-02-01

264

Accelerated laboratory weathering of acrylic lens materials  

NASA Astrophysics Data System (ADS)

Flat samples from PMMA formulations were subjected to accelerated laboratory weathering in an "Atlas Xenotest Alpha +" weathering device operating at 3 Sun irradiance. Measured properties included transmittance, yellowness index, haze and molecular weight. All samples remained transparent after 3.2GJ/m2 radiant exposure (300 - 400nm). Other observations were a reduction of transmittance, an increase of yellowness index and a reduction of molecular weight. The amount of change depended on the PMMA formulation. Higher UV absorber concentrations led to smaller changes in optical properties and molecular weight. First data obtained from EMMAQUA accelerated outdoor exposure showed much smaller changes in optical properties than Alpha weathering data of equal radiant exposures. Data from Alpha exposure at lower temperatures underline the role of temperature as a second acceleration factor.

Arndt, Thomas; Richter, Steffen; Pasierb, Mike

2013-09-01

265

Ultra accelerated testing of PV module components  

SciTech Connect

Using concentrated natural sunlight at the NREL High Flux Solar Furnace, we have exposed several materials to acceleration factors of up to 400 times the normal outdoor UV exposure dose. This accelerated rate allows the exposure of materials such that a year of outdoor exposure can be simulated in about 5 hours. We have studied the solarization of cerium containing glass, the degradation of ethylene vinyl acetate laminated between borosilicate glass, and the yellowing of standard polystyrene test coupons. The first two candidates are of interest to the photovoltaics (PV) program, and the last candidate material is a widely used dosimeter for ultra violet (UV) exposure in accelerated weathering chambers. {copyright} {ital 1999 American Institute of Physics.}

Pitts, J.R.; King, D.E.; Bingham, C.; Czanderna, A.W. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 (United States)

1999-03-01

266

Ring accelerators  

SciTech Connect

We present two-dimensional simulations in (r-z) and r-theta) cylinderical geometries of imploding-liner-driven accelerators of rings of charged particles. We address issues of azimuthal and longitudinal stability of the rings. We discuss self-trapping designs in which beam injection and extraction is aided by means of external cusp fields. Our simulations are done with the 2-1/2-D particle-in-cell plasma simulation code CLINER, which combines collisionless, electromagnetic PIC capabilities with a quasi-MHD finite element package.

Gisler, G.; Faehl, R.

1983-01-01

267

Human exposure to styrene  

Microsoft Academic Search

An industrial hygiene study of 10 glassfiber reinforced polyester plants (including 90 workers) was undertaken to investigate the styrene exposure in this industry and to estimate biological limit values (BLV's) for the urinary metabolites of styrene: mandelic (MA) and phenylglyoxylic acids (PGA). Time weighted average (TWA) styrene exposures were found ranging from 2 to 200 ppm. The urinary elimination of

Michel P. Guillemin; Daniel Bauer; Brigitte Martin; Alfio Marazzi

1982-01-01

268

Plasma accelerators; Plazmennye uskoriteli  

Microsoft Academic Search

Papers concerning the physical processes in plasma accelerators are ; included, covering some specific accelerator types, magnetic plasma compressors, ; plasma diagnostics methods, and plasma accelerator applications in thermonuclear ; studies, gasdynamics, and space studies. The topics also include plasma ; acceleration control problems, high-vacuum technology, plasma accelerator designs ; with narrow and broad acceleration zones, and electrode processes in

Artsimovich

1973-01-01

269

Space charge compensation in laser particle accelerators  

NASA Astrophysics Data System (ADS)

Laser particle acceleration (LPA) involves the acceleration of particle beams by electromagnetic waves with relatively short wavelength compared with conventional radio-frequency systems. These short length scales raise the question whether space charge effects may be a limiting factor in LPA performance. This is analyzed in two parts of an accelerator system, the acceleration sections and the drift region of the prebuncher. In the prebuncher, space charge can actually be converted to an advantage for minimizing the energy spread. In the accelerator sections, the laser fields can compensate for space charge forces, but the compensation becomes weaker for high beam energy.

Steinhauer, L. C.; Kimura, W. D.

1999-07-01

270

Occupational exposure to crystalline silica and autoimmune disease.  

PubMed Central

Occupational exposure to silica dust has been examined as a possible risk factor with respect to several systemic autoimmune diseases, including scleroderma, rheumatoid arthritis, systemic lupus erythematosus, and some of the small vessel vasculitidies with renal involvement (e.g., Wegener granulomatosis). Crystalline silica, or quartz, is an abundant mineral found in sand, rock, and soil. High-level exposure to respirable silica dust can cause chronic inflammation and fibrosis in the lung and other organs. Studies of specific occupational groups with high-level silica exposure (e.g., miners) have shown increased rates of autoimmune diseases compared to the expected rates in the general population. However, some clinic- and population-based studies have not demonstrated an association between silica exposure and risk of autoimmune diseases. This lack of effect may be due to the limited statistical power of these studies to examine this association or because the lower- or moderate-level exposures that may be more common in the general population were not considered. Experimental studies demonstrate that silica can act as an adjuvant to nonspecifically enhance the immune response. This is one mechanism by which silica might be involved in the development of autoimmune diseases. Given that several different autoimmune diseases may be associated with silica dust exposure, silica dust may act to promote or accelerate disease development, requiring some other factor to break immune tolerance or initiate autoimmunity. The specific manifestation of this effect may depend on underlying differences in genetic susceptibility or other environmental exposures.

Parks, C G; Conrad, K; Cooper, G S

1999-01-01

271

Guiding and Ionization Blueshift in Ablative Capillary Waveguide Accelerators  

Microsoft Academic Search

Laser wakefield acceleration (LWFA) in plasmas has been demonstrated with gradients which are orders of magnitude greater than the limit on conventional Radio Frequency accelerators. However, the acceleration length is limited by two factors, the dephasing length and the Rayleigh range of the laser pulse. Dephasing length is the distance in which electrons overtake the laser pulse and can be

Chris McGuffey; Takeshi Matsuoka; Michael Levin; Stepan Bulanov; Vladimir Chvykov; Galina Kalintchenko; Pascal Rousseau; Victor Yanovsky; Arie Zigler; Anatoly Maksimchuk; Karl Krushelnick

2009-01-01

272

Accelerating projects  

SciTech Connect

This chapter describes work at ORNL in the period around 1950, when the laboratory was evolving from its original mission of research aimed at producing the atomic bomb, to a new mission, which in many ways was unclear. The research division from Y-12 merged with the laboratory, which gave an increased work force, access to a wide array of equipment, and the opportunity to work on a number of projects related to nuclear propulsion. The first major project was for a nuclear aircraft. From work on this program, a good share of the laboratories work in peaceful application of nuclear energy would spring. A major concern was the development of light weight shielding to protect the crew and materials in such a plane. To do such shielding work, the laboratory employed existing, and new reactors. The original plans called for the transfer of reactor work to Argonne, but because of their own research load, and the needs of the lab, new reactor projects were started at the lab. They included the Low Intensity Test Reactor, the Swimming Pool Reactor, the Bulk Shielding Reactor, the Tower Shielding Facility, and others. The laboratory was able to extend early work on calutrons to accelerator development, pursuing both electrostatic accelerators and cyclotrons. The aircraft project also drove the need for immense quantities of scientific data, with rapid analysis, which resulted the development of divisions aimed at information support and calculational support. The laboratory also expanded its work in the effects of radiation and cells and biological systems, as well as in health physics.

Not Available

1992-01-01

273

Nonionizing Radiation Around Linear Accelerators  

Microsoft Academic Search

The World Health Organization, the International Radiation Protection Association (IRPA), and the American Conference of Governmental Industrial Hygienists have recommended using time-weighted and time-dependent standards for nonionizing radiation exposure assessment. Such hygienic norms have been developed on the basis of the electromagnetic energy evaluation. Two Varian linear accelerators, Clinac 1800 and Clinac 6X, were examined for different nonionizing radiation hazards.

Michel S. Israel; Yona Mahler; Dan Blau; Ezra Levinger

1995-01-01

274

Shielding design of a treatment room for an accelerator-based epithermal neutron irradiation facility for BNCT  

Microsoft Academic Search

Protecting the facility personnel and the general public from radiation exposure is a primary safety concern of an accelerator-based epithermal neutron irradiation facility. This work makes an attempt at answering the questions {open_quotes}How much?{close_quotes} and {open_quotes}What kind?{close_quotes} of shielding will meet the occupational limits of such a facility. Shielding effectiveness is compared for ordinary and barytes concretes in combination with

Jeffrey F. Evans; Thomas E. Blue

1996-01-01

275

A laser-plasma accelerator producing monoenergetic electron beams  

Microsoft Academic Search

Particle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeVm-1, owing to material breakdown at the walls of the structure. Thus, the production of energetic particle beams currently requires large-scale accelerators and expensive infrastructures. Laser-plasma accelerators have been

J. Faure; Y. Glinec; A. Pukhov; S. Kiselev; S. Gordienko; E. Lefebvre; J.-P. Rousseau; F. Burgy; V. Malka

2004-01-01

276

Teleportation of accelerated information  

NASA Astrophysics Data System (ADS)

A theoretical quantum teleportation protocal is suggested to teleport accelerated and non-accelerated information over different classes of accelerated quantum channels. For the accelerated information, it is shown that the fidelity of the teleported state increases as the entanglement of the initial quantum channel increases. However as the difference between the accelerated channel and the accelerated information decreases the fidelity increases. The fidelity of the non accelerated information increases as the entanglement of the initial quantum channel increases, while the accelerations of the quantum channel has a little effect. The possibility of sending quantum information over accelerated quantum channels is much better than sending classical information.

Metwally, Nasser

2013-01-01

277

High average power induction accelerators  

SciTech Connect

The induction accelerator is discussed with respect to general background and concept, beam transport, scaling, pulse power technology, and the electron beam injector. A discussion of the factors which affect the scaling of the intensity of the beam is given. Limiting factors include collective forces in the beam, virtual cathode formation, surroundings, and beam breakup instability. 24 refs., 11 figs. (WRF)

Swingle, J.C. (ed.)

1985-10-01

278

Operational Radiation Protection in High-Energy Physics Accelerators: Implementation of ALARA in Design and Operation of Accelerators  

SciTech Connect

It used to happen often, to us accelerator radiation protection staff, to be asked by a new radiation worker: ?How much dose am I still allowed?? And we smiled looking at the shocked reaction to our answer: ?You are not allowed any dose?. Nowadays, also thanks to improved training programs, this kind of question has become less frequent, but it is still not always easy to convince workers that staying below the exposure limits is not sufficient. After all, radiation is still the only harmful agent for which this is true: for all other risks in everyday life, from road speed limits to concentration of hazardous chemicals in air and water, compliance to regulations is ensured by keeping below a certain value. It appears that a tendency is starting to develop to extend the radiation approach to other pollutants (1), but it will take some time before the new attitude makes it way into national legislations.

Fasso, A.; Rokni, S.; /SLAC

2011-06-30

279

Linear Accelerator (LINAC)  

MedlinePLUS

... of page • Equipment View larger with caption The linear accelerator uses microwave technology (similar to that used for radar) to accelerate electrons in a part of the accelerator called the "wave guide," then allows these electrons to collide with ...

280

Effects of a Commercial Drink on Acceleration Tolerance and Cognitive Performance.  

National Technical Information Service (NTIS)

This study examined the ability of a commercial energy drink to enhance acceleration tolerance, strength under G-load, and cognitive performance immediately prior to and following acceleration exposure. Eight experienced centrifuge subjects completed thre...

G. L. Warren J. Fischer T. B. Walker U. Balldin W. Storm

2009-01-01

281

Very High Pulse-Energy Accelerators.  

National Technical Information Service (NTIS)

The dominant trend in the development of pulsed power accelerator technology over the last decade has been towards higher power and shorter pulse widths. Limitations in high voltage, high current switch performance, and in power flow through vacuum insula...

J. J. Ramirez

1989-01-01

282

Photonic Acceleration in Astrophysics  

NASA Astrophysics Data System (ADS)

Gamma Ray Bursts (GRB) deliver very high intensity photons with energies from 10 keV to over 100 MeV at a irradiance of 10^30 (30 km/R)^2 Watt/cm^2. This is in the nonlinear QED regime and the induced wakefield is close to the Schwinger field (E ~^16 V/cm). Protons and electrons can be accelerated in such a strong field to 10^21 eV/km in the vicinity of the GRB source. The maximum acceleration is limited by the critical Schwinger field times the length of the field: q ( E (= 10^16.5 V/cm) ( L ((1000 km) = 10^24 eV. Trains of such wakefields are expected in the outflow of photons from GRB's, which gives a Chapman-Kolmogorov type power energy spectrum [Chandrasekhar, 1953; Mima et al. 1991], which is close to a Bremsstrahlung-type spectrum, f(E) = E^-a (a = 1). Some of the accelerated protons can have energies as high as 10^23 eV. The secondary pions and their daughters (neutrinos) that may be produced in-situ near the acceleration site of the GRB can have energies around 10^22 eV (= 1.6 ( 10^10 erg). The neutrino flux from the semi-daily occurrence of GRB's (with energy output of ~ 10^52 erg can provide a flux of high intensity EHE neutrinos in the universe as a function of the acceleration efficiency coefficient (k): I( (E ( 10^21 eV) = 5k (10^52 eV)/(1.6 ( 10^10 erg)/4(pi)R^2/day = 1 /km^2 yr (for k = 1% *). *(cf. Laser wakefield experiments with Petawatt indicated k = 5 ~ 10% for protons [M. Key, 1999].) A compact photonic acceleration mechanism is thus suggested as a candidate for the origin of extremely high energy cosmic rays (EECR). Observed characteristics of EECR beyond energies of several 1019 eV pose a number of challenges and opportunities for physics and astrophysics. Foremost among them is the apparent defiance or violation of the proton energy cutoff of Greisen-Zatsepin-Kuzmin (GZK). The other is the apparent correlation in some of ECR events. And the most important is the difficulty to accelerate particles by the conventional Fermi mechanism to reach such high energies. We suggest that the intense photon flux emanating from a gamma ray burst is capable of yielding a sufficiently robust and rugged plasma structure suitable to accelerate protons and other charged particles to extreme high energies ( ~ 10^22 eV) over thousands of kilometers in the GRB atmosphere. Photon flux above a certain threshold can self-modulate in the plasma to create longitudinal (as well as transverse) structures that help snowplow and accelerate charged particles. The sustained large flux of photons maintains the acceleration by successive flux to repeat the process once a particular class of photons give up energies to particles and red-shift. The decrease of plasma density away from the GRB further facilitates this process, providing ever greater coherence (acceleration) length. The stochastic repetition of this process yields a power-law energy spectrum with an exponent of -1. Such compact prompt intense acceleration of protons in the vicinity of GRB manifests through neutrinos (by proton-proton or proton-photon collisions near GRB). These neutrinos can propagate over a cosmological distance without decay or loss until reaching and colliding with relic neutrinos in our Super-Cluster (Virgo), eventually converting themselves into EECR particles such as protons and photons of energies of ~ 10^20 eV. The estimated neutrino energy flux and spectrum are consistent with observation and have a number of implications on EHECR, cosmological origin, and neutrino physics. Other high field astronomical sites such as the core and jets of Active Galactic Nuclei can have lesser but similar accelerations.

Takahashi, Yoshiyuki

2000-04-01

283

Weak-chaos ratchet accelerator  

NASA Astrophysics Data System (ADS)

Classical Hamiltonian systems with a mixed phase space and some asymmetry may exhibit chaotic ratchet effects. The most significant such effect is a directed momentum current or acceleration. In known model systems, this effect may arise only for sufficiently strong chaos. In this paper, a Hamiltonian ratchet accelerator is introduced, featuring a momentum current for arbitrarily weak chaos. The system is a realistic, generalized kicked rotor and is exactly solvable to some extent, leading to analytical expressions for the momentum current. While this current arises also for relatively strong chaos, the maximal current is shown to occur, at least in one case, precisely in a limit of arbitrarily weak chaos.

Dana, Itzhack; Roitberg, Vladislav B.

2011-06-01

284

Six-degree-of-freedom whole-body vibration exposure levels during routine skidder operations.  

PubMed

This research focuses on quantifying six-degree-of-freedom (6-DOF) whole-body vibration (WBV) exposure levels that occur in Northern Ontario skidders during routine field operating tasks. 6-DOF vibration running root-mean-square (RMS) acceleration levels at the operator/seat interface were determined for eight skidders while driving loaded, driving unloaded, picking up a load, dropping off a load and ploughing logs under field operating conditions. The acceleration data were weighted in accordance with ISO 2631-1:1997 and evaluated for both health and comfort outcomes. The mean running RMS weighted translational and rotational accelerations all exceeded 0.36 m/s(2) and 0.14 rad/s(2). The greatest average accelerations occurred while driving unloaded with this condition displaying translational vibration total values (VTV) that exceeded the upper limit of the ISO 2631-1:1997 health caution zone within an average of 2.3 h. Utilizing 6-DOF VTV, virtually all operating conditions would be designated as uncomfortable. STATEMENT OF RELEVANCE: This study provides one of the most comprehensive reports on vibration exposures in seated vehicle operators. The results are geared towards ergonomists with discussions on health effects and measurement concerns, while providing the raw vibration exposure data that will be useful to vehicle, component and vibration sensor designers. PMID:20432089

Jack, R J; Oliver, M; Dickey, J P; Cation, S; Hayward, G; Lee-Shee, N

2010-05-01

285

Accelerators for nuclear physics  

Microsoft Academic Search

This article describes the principal charged particle accelerators being used today for research in nuclear physics in the energy range up to about 1000 MeV. The accelerators include Van de Graaffs, sector cyclotrons and linear accelerators for both positive ions and electrons. For each type of accelerator a brief treatment is given of the recent history, operating principles, some special

D J Clark

1972-01-01

286

Future accelerator technology  

SciTech Connect

A general discussion is presented of the acceleration of particles. Upon this foundation is built a categorization scheme into which all accelerators can be placed. Special attention is devoted to accelerators which employ a wake-field mechanism and a restricting theorem is examined. It is shown how the theorem may be circumvented. Comments are made on various acceleration schemes.

Sessler, A.M.

1986-05-01

287

Accelerator-driven Transmutation of Waste  

NASA Astrophysics Data System (ADS)

Nuclear waste from commercial power plants contains large quantities of plutonium, other fissionable actinides, and long-lived fission products that are potential proliferation concerns and create challenges for the long-term storage. Different strategies for dealing with nuclear waste are being followed by various countries because of their geologic situations and their views on nuclear energy, reprocessing and non-proliferation. The current United States policy is to store unprocessed spent reactor fuel in a geologic repository. Other countries are opting for treatment of nuclear waste, including partial utilization of the fissile material contained in the spent fuel, prior to geologic storage. Long-term uncertainties are hampering the acceptability and eventual licensing of a geologic repository for nuclear spent fuel in the US, and driving up its cost. The greatest concerns are with the potential for radiation release and exposure from the spent fuel for tens of thousands of years and the possible diversion and use of the actinides contained in the waste for weapons construction. Taking advantage of the recent breakthroughs in accelerator technology and of the natural flexibility of subcritical systems, the Accelerator-driven Transmutation of Waste (ATW) concept offers the United States and other countries the possibility to greatly reduce plutonium, higher actinides and environmentally hazardous fission products from the waste stream destined for permanent storage. ATW does not eliminate the need for, but instead enhances the viability of permanent waste repositories. Far from being limited to waste destruction, the ATW concept also brings to the table new technologies that could be relevant for next-generation power producing reactors. In the ATW concept, spent fuel would be shipped to the ATW site where the plutonium, transuranics and selected long-lived fission products would be destroyed by fission or transmutation in their first and only pass through the facility, using an accelerator-driven subcritical burner cooled by liquid lead/bismuth and limited pyrochemical treatment of the spent fuel and residual waste. This approach contrasts with the present-day practices of aqueous reprocessing (Europe and Japan), in which high purity plutonium is produced and used in the fabrication of fresh mixed oxide fuel (MOX) that is shipped off-site for use in light water reactors.

Venneri, Francesco

1998-04-01

288

Repair of overheating linear accelerator  

SciTech Connect

Los Alamos Neutron Science Center (LANSCE) is a proton accelerator that produces high energy particle beams for experiments. These beams include neutrons and protons for diverse uses including radiography, isotope production, small feature study, lattice vibrations and material science. The Drift Tube Linear Accelerator (DTL) is the first portion of a half mile long linear section of accelerator that raises the beam energy from 750 keV to 100 MeV. In its 31st year of operation (2003), the DTL experienced serious issues. The first problem was the inability to maintain resonant frequency at full power. The second problem was increased occurrences of over-temperature failure of cooling hoses. These shortcomings led to an investigation during the 2003 yearly preventative maintenance shutdown that showed evidence of excessive heating: discolored interior tank walls and coper oxide deposition in the cooling circuits. Since overheating was suspected to be caused by compromised heat transfer, improving that was the focus of the repair effort. Investigations revealed copper oxide flow inhibition and iron oxide scale build up. Acid cleaning was implemented with careful attention to protection of the base metal, selection of components to clean and minimization of exposure times. The effort has been very successful in bringing the accelerator through a complete eight month run cycle allowing an incredible array of scientific experiments to be completed this year (2003-2004). This paper will describe the systems, investigation analysis, repair, return to production and conclusion.

Barkley, Walter; Baldwin, William; Bennett, Gloria; Bitteker, Leo; Borden, Michael; Casados, Jeff; Fitzgerald, Daniel; Gorman, Fred; Johnson, Kenneth; Kurennoy, Sergey; Martinez, Alberto; O’Hara, James; Perez, Edward; Roller, Brandon; Rybarcyk, Lawrence; Stark, Peter; Stockton, Jerry

2004-01-01

289

Transverse electron resonance accelerator  

SciTech Connect

Transverse (to the velocity, v, of the particles to be accelerated) electron oscillations are generated in high (e.g. solid) density plasmas by either an electromagnetic wave or by the field of charged particles traveling parallel to v. The generating field oscillates with frequency ..omega.. = ..omega../sub p/, where ..omega../sub p/ is the plasma frequency. The plasma is confined to a sequence of microstructures with typical dimensions of d approx. = 2..pi..c/..omega../sub p/, allowing the generating fields to penetrate. Since ..omega../sub p/ is now high, the time scales, T, are correspondingly reduced. The microstructures are allowed to explode after t = T, until then they are confined by ion inertia. As a result of resonance, the electric field, E, inside the microstructures can exceed the generating field E/sub L/. The generating force is proportional to E/sub L/ (as opposed to E/sub L//sup 2/). Phase matching of particles is possible by appropriate spacing of the microstructures or by a gas medium. The generating beam travels outside the plasma, filamentation is not a problem. The mechanism is relatively insensitive to the exact shape and position of the microstructures. This device contains features of various earlier proposed acceleration mechanisms and may be considered as the limiting case of several of those for small d, T and high E.

Csonka, P.L.

1985-01-01

290

Theory of intrabeam scattering in strong-focussing accelerators  

Microsoft Academic Search

Intrabeam scattering is the ultimate limitation on the luminosities of high energy proton and heavy ion accelerators. We review the theory of intrabeam scattering from the earliest theory, which was applicable to weak-focusing accelerators, to the latest strong-focussing theory proposed by Bjorken and Mtingwa. Comparisons of the theory to experimental data at several accelerators are given. Moreover, predictions are made

Mtingwa

1988-01-01

291

Establishing the Biodynamics Data Resource (BDR): Human Volunteer Impact Acceleration Research Data in the BDR.  

National Technical Information Service (NTIS)

One of the most noteworthy collections of impact exposure data was generated at the U.S. Naval Biodynamics Laboratory (NBDL). Over 25 years, NBDL conducted thousands of impact acceleration exposures with hundreds of human research volunteers. The resultin...

A. E. Austermann A. L. Schmidt B. S. Shender K. B. Vasquez V. C. Chancey

2010-01-01

292

Current limiters  

SciTech Connect

The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.

Loescher, D.H. [Sandia National Labs., Albuquerque, NM (United States). Systems Surety Assessment Dept.; Noren, K. [Univ. of Idaho, Moscow, ID (United States). Dept. of Electrical Engineering

1996-09-01

293

Superconducting cavities for particle accelerators  

NASA Astrophysics Data System (ADS)

RF Superconductivity has become an important technology for particle accelerators for high energy physics, nuclear physics, and free electron lasers. More than 100 MVolts of Superconducting RF (SRF) cavities have been installed in accelerators for heavy ions and operated at gradients of 2-3 MV/m in excess of 105 hours. More than 500 MVolts are installed in electron accelerators and operated at gradients of 4-6 MV/m in excess of 104 hours. Encouraged by this success, another 500 meters of SRF cavities are in the production line. New applications for High Energy Physics are forthcoming for high current e+e- colliders in the B-quark energy range (B-factory). For the next linear collider in the TeV energy range, there are many compelling attractions to use SRF, if the gradients can be improved substantially and the costs lowered. Substantial progress has been made in understanding performance limitations and in inventing cures through better cavity geometries, materials, and processes. Techniques are now in hand to reach 15-20 MV/m accelerating. In light of this progress, the potential of high gradient SRF for a TeV Energy Superconducting Linear Accelerator (TESLA) will be explored.

Padamsee, H.

1992-02-01

294

Head impact exposure in collegiate football players  

Microsoft Academic Search

In American football, impacts to the helmet and the resulting head accelerations are the primary cause of concussion injury and potentially chronic brain injury. The purpose of this study was to quantify exposures to impacts to the head (frequency, location and magnitude) for individual collegiate football players and to investigate differences in head impact exposure by player position. A total

Joseph J. Crisco; Bethany J. Wilcox; Jonathan G. Beckwith; Jeffrey J. Chu; Ann-Christine Duhaime; Steven Rowson; Stefan M. Duma; Arthur C. Maerlender; Thomas W. McAllister; Richard M. Greenwald

2011-01-01

295

Radiation risk management at DOE accelerator facilities  

SciTech Connect

The DOE accelerator contractors have been discussing among themselves and with the Department how to improve radiation safety risk management. This activity-how to assure prevention of unplanned high exposures-is separate from normal exposure management, which historically has been quite successful. The ad-hoc Committee on the Accelerator Safety Order and Guidance [CASOG], formed by the Accelerator Section of the HPS, has proposed a risk- based approach, which will be discussed. Concepts involved are risk quantification and comparison (including with non-radiation risk), passive and active (reacting) protection systems, and probabilistic analysis. Different models of risk management will be presented, and the changing regulatory environment will also be discussed..

Dyck, O.B. van

1997-01-01

296

Accelerator physics model of expected beam loss along the sns accelerator facility during normal operation.  

National Technical Information Service (NTIS)

The most demanding requirement in the design of the SNS accelerator chain is to keep the accelerator complex under hands-on maintenance. This requirement implies a hard limit for residual radiation below 100 mrem/hr at one feet from the vacuum pipe and fo...

Catalan Lasheras Cousineau Galambos Holtkamp Raparia Shafer Staples Stovall Tanke Wangler Wei

2002-01-01

297

Remote handling and accelerators  

SciTech Connect

The high-current levels of contemporary and proposed accelerator facilities induce radiation levels into components, requiring consideration be given to maintenance techniques that reduce personnel exposure. Typical components involved include beamstops, targets, collimators, windows, and instrumentation that intercepts the direct beam. Also included are beam extraction, injection, splitting, and kicking regions, as well as purposeful spill areas where beam tails are trimmed and neutral particles are deposited. Scattered beam and secondary particles activate components all along a beamline such as vacuum pipes, magnets, and shielding. Maintenance techniques vary from hands-on to TV-viewed operation using state-of-the-art servomanipulators. Bottom- or side-entry casks are used with thimble-type target and diagnostic assemblies. Long-handled tools are operated from behind shadow shields. Swinging shield doors, unstacking block, and horizontally rolling shield roofs are all used to provide access. Common to all techniques is the need to make operations simple and to provide a means of seeing and reaching the area.

Wilson, M.T.

1983-01-01

298

Charged Particle Acceleration by Lasers in Plasmas  

SciTech Connect

Several physical processes of laser electron acceleration in plasmas are revisited. A laser beam can drive plasma waves which in turn can accelerate resonant electrons. If these plasma waves can reach amplitude limited only by wave breaking alone, then the corresponding accelerating gradient in the plasma wave is of the order of electron rest mass energy per plasma skin depth, typically about GEV per centimeter. This is several orders of magnitudes higher than the conventional RF field gradient, giving rise to the possibility of compact accelerators needed for high energy physics research as well as medical and other applications. The chirped short pulse laser, with intensity exceeding the threshold for relativistic self focusing, can generate ion bubble in its wake by expelling electrons. The electrons at the bubble boundary, surge toward the stagnation point and pile up there. As the pile acquires a critical size, these electrons are injected into the bubble and accelerated by the combined fields of ion space charge and the plasma wave to Gev in energy. Most remarkably these electrons are bunched in phase space while being accelerated to high energy, resulting in near mono-energetic electron beam of high beam quality, with narrow energy spread. We review also other processes related to laser electron acceleration, such as acceleration in plasma wave assisted by ponderomotive force and betatron acceleration.

Liu, C. S.; Tripathi, V. K. [Department of Physics, University of Maryland, College Park, MD 20742 (United States)

2007-07-11

299

Charged Particle Acceleration by Lasers in Plasmas  

NASA Astrophysics Data System (ADS)

Several physical processes of laser electron acceleration in plasmas are revisited. A laser beam can drive plasma waves which in turn can accelerate resonant electrons. If these plasma waves can reach amplitude limited only by wave breaking alone, then the corresponding accelerating gradient in the plasma wave is of the order of electron rest mass energy per plasma skin depth, typically about GEV per centimeter. This is several orders of magnitudes higher than the conventional RF field gradient, giving rise to the possibility of compact accelerators needed for high energy physics research as well as medical and other applications. The chirped short pulse laser, with intensity exceeding the threshold for relativistic self focusing, can generate ion bubble in its wake by expelling electrons. The electrons at the bubble boundary, surge toward the stagnation point and pile up there. As the pile acquires a critical size, these electrons are injected into the bubble and accelerated by the combined fields of ion space charge and the plasma wave to Gev in energy. Most remarkably these electrons are bunched in phase space while being accelerated to high energy, resulting in near mono-energetic electron beam of high beam quality, with narrow energy spread. We review also other processes related to laser electron acceleration, such as acceleration in plasma wave assisted by ponderomotive force and betatron acceleration.

Liu, C. S.; Tripathi, V. K.

2007-07-01

300

Report on accelerated corrosion studies.  

SciTech Connect

Sandia National Laboratories (SNL) conducted accelerated atmospheric corrosion testing for the U.S. Consumer Product Safety Commission (CPSC) to help further the understanding of the development of corrosion products on conductor materials in household electrical components exposed to environmental conditions representative of homes constructed with problem drywall. The conditions of the accelerated testing were chosen to produce corrosion product growth that would be consistent with long-term exposure to environments containing humidity and parts per billion (ppb) levels of hydrogen sulfide (H{sub 2}S) that are thought to have been the source of corrosion in electrical components from affected homes. This report documents the test set-up, monitoring of electrical performance of powered electrical components during the exposure, and the materials characterization conducted on wires, screws, and contact plates from selected electrical components. No degradation in electrical performance (measured via voltage drop) was measured during the course of the 8-week exposure, which was approximately equivalent to 40 years of exposure in a light industrial environment. Analyses show that corrosion products consisting of various phases of copper sulfide, copper sulfate, and copper oxide are found on exposed surfaces of the conductor materials including wires, screws, and contact plates. The morphology and the thickness of the corrosion products showed a range of character. In some of the copper wires that were observed, corrosion product had flaked or spalled off the surface, exposing fresh metal to the reaction with the contaminant gasses; however, there was no significant change in the wire cross-sectional area.

Mowry, Curtis Dale; Glass, Sarah Jill; Sorensen, Neil Robert

2011-03-01

301

Using Accelerated Testing to Predict Module Reliability  

SciTech Connect

Long-term reliability is critical to the cost effectiveness and commercial success of photovoltaic (PV) products. Today most PV modules are warranted for 25 years, but there is no accepted test protocol to validate a 25-year lifetime. The qualification tests do an excellent job of identifying design, materials, and process flaws that are likely to lead to premature failure (infant mortality), but they are not designed to test for wear-out mechanisms that limit lifetime. This paper presents a method for evaluating the ability of a new PV module technology to survive long-term exposure to specific stresses. The authors propose the use of baseline technologies with proven long-term field performance as controls in the accelerated stress tests. The performance of new-technology modules can then be evaluated versus that of proven-technology modules. If the new-technology demonstrates equivalent or superior performance to the proven one, there is a high likelihood that they will survive versus the tested stress in the real world.

Wohlgemuth, J. H.; Kurtz, S.

2011-01-01

302

Accelerator mass spectrometry of plutonium isotopes  

Microsoft Academic Search

The feasibility of measuring plutonium isotope ratios by accelerator mass spectrometry has been demonstrated. Measurements on a test sample of known composition and on a blank showed that isotope ratios could be determined quantitatively, and that the present limit of detection by AMS is ? 106 atoms of plutonium. For 239Pu, this limit is at least two orders of magnitude

L. K. Fifield; R. G. Cresswell; M. L. di Tada; T. R. Ophel; J. P. Day; A. P. Clacher; S. J. King; N. D. Priest

1996-01-01

303

Lasers and new methods of particle acceleration  

SciTech Connect

There has been a great progress in development of high power laser technology. Harnessing their potential for particle accelerators is a challenge and of great interest for development of future high energy colliders. The author discusses some of the advances and new methods of acceleration including plasma-based accelerators. The exponential increase in sophistication and power of all aspects of accelerator development and operation that has been demonstrated has been remarkable. This success has been driven by the inherent interest to gain new and deeper understanding of the universe around us. With the limitations of the conventional technology it may not be possible to meet the requirements of the future accelerators with demands for higher and higher energies and luminosities. It is believed that using the existing technology one can build a linear collider with about 1 TeV center of mass energy. However, it would be very difficult (or impossible) to build linear colliders with energies much above one or two TeV without a new method of acceleration. Laser driven high gradient accelerators are becoming more realistic and is expected to provide an alternative, (more compact, and more economical), to conventional accelerators in the future. The author discusses some of the new methods of particle acceleration, including laser and particle beam driven plasma based accelerators, near and far field accelerators. He also discusses the enhanced IFEL (Inverse Free Electron Laser) and NAIBEA (Nonlinear Amplification of Inverse-Beamstrahlung Electron Acceleration) schemes, laser driven photo-injector and the high energy physics requirements.

Parsa, Z.

1998-02-01

304

Collective Acceleration of Ions.  

National Technical Information Service (NTIS)

The collective method for acceleration of ions is described. The problem of the formation of an electron ring cluster charged with ions, its stability and focusing, and some questions of acceleration are discussed. (Author)

A. B. Kuznetsov E. A. Parelshtein I. N. Ivanov K. A. R. Reshetnikov V. A. Preizendorf

1973-01-01

305

Acceleration of Gravity 1  

NSDL National Science Digital Library

This lab is a Level 2 inquiry activity that should be taught after students understand acceleration but before they learn the equations for calculating the acceleration of a body dropped from a certain height. After this activity, students should understa

Horton, Michael

2009-05-30

306

Accelerator Technology Division  

NASA Astrophysics Data System (ADS)

In fiscal year (FY) 1991, the Accelerator Technology (AT) division continued fulfilling its mission to pursue accelerator science and technology and to develop new accelerator concepts for application to research, defense, energy, industry, and other areas of national interest. This report discusses the following programs: The Ground Test Accelerator Program; APLE Free-Electron Laser Program; Accelerator Transmutation of Waste; JAERI, OMEGA Project, and Intense Neutron Source for Materials Testing; Advanced Free-Electron Laser Initiative; Superconducting Super Collider; The High-Power Microwave Program; (Phi) Factory Collaboration; Neutral Particle Beam Power System Highlights; Accelerator Physics and Special Projects; Magnetic Optics and Beam Diagnostics; Accelerator Design and Engineering; Radio-Frequency Technology; Free-Electron Laser Technology; Accelerator Controls and Automation; Very High-Power Microwave Sources and Effects; and GTA Installation, Commissioning, and Operations.

1992-04-01

307

Validation of Force Limited Vibration Testing Using Dummy Satellite Structure  

Microsoft Academic Search

The benefit of force limited testing is that it limits the overtesting of flight hardware, by controlling input force and acceleration from the shaker to the test article. The force limited vibration testing is developed to minimize the overtesting associated with enveloping the acceleration spectral density and differences in flight versus test mounting impedance. This paper reports the basic study

K. Nagahama; Q. Shi; S. Ando; H. Saegusa

2004-01-01

308

Nonparaxial Mathieu and Weber Accelerating Beams  

NASA Astrophysics Data System (ADS)

We demonstrate both theoretically and experimentally nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of previously found accelerating beams. We show that such beams bend into large angles along circular, elliptical, or parabolic trajectories but still retain nondiffracting and self-healing capabilities. The circular nonparaxial accelerating beams can be considered as a special case of the Mathieu accelerating beams, while an Airy beam is only a special case of the Weber beams at the paraxial limit. Not only do generalized nonparaxial accelerating beams open up many possibilities of beam engineering for applications, but the fundamental concept developed here can be applied to other linear wave systems in nature, ranging from electromagnetic and elastic waves to matter waves.

Zhang, Peng; Hu, Yi; Li, Tongcang; Cannan, Drake; Yin, Xiaobo; Morandotti, Roberto; Chen, Zhigang; Zhang, Xiang

2012-11-01

309

Accelerated large-scale multiple sequence alignment  

PubMed Central

Background Multiple sequence alignment (MSA) is a fundamental analysis method used in bioinformatics and many comparative genomic applications. Prior MSA acceleration attempts with reconfigurable computing have only addressed the first stage of progressive alignment and consequently exhibit performance limitations according to Amdahl's Law. This work is the first known to accelerate the third stage of progressive alignment on reconfigurable hardware. Results We reduce subgroups of aligned sequences into discrete profiles before they are pairwise aligned on the accelerator. Using an FPGA accelerator, an overall speedup of up to 150 has been demonstrated on a large data set when compared to a 2.4 GHz Core2 processor. Conclusions Our parallel algorithm and architecture accelerates large-scale MSA with reconfigurable computing and allows researchers to solve the larger problems that confront biologists today. Program source is available from http://dna.cs.byu.edu/msa/.

2011-01-01

310

Acceleration: It's Elementary  

ERIC Educational Resources Information Center

Acceleration is one tool for providing high-ability students the opportunity to learn something new every day. Some people talk about acceleration as taking a student out of step. In actuality, what one is doing is putting a student in step with the right curriculum. Whole-grade acceleration, also called grade-skipping, usually happens between…

Willis, Mariam

2012-01-01

311

Hig accelerator system  

Microsoft Academic Search

The design criteria and operational capabilities of the Hi-g accelerator system, a pneumatically operated device are described. The system was designed to accelerate an experiment package up the experimental tube of the Sandia Annular Core Pulse Reactor. A variety of experimental sizes can be accommodated by the system and a wide range of acceleration levels is possible.

J. P. Atencio

1976-01-01

312

Acceleration: It's Elementary  

ERIC Educational Resources Information Center

|Acceleration is one tool for providing high-ability students the opportunity to learn something new every day. Some people talk about acceleration as taking a student out of step. In actuality, what one is doing is putting a student in step with the right curriculum. Whole-grade acceleration, also called grade-skipping, usually happens between…

Willis, Mariam

2012-01-01

313

Direction of Acceleration  

NSDL National Science Digital Library

In this short lab, students observe the movement of an air bubble in a small level, attached to a toy truck, as it is moved from a stop, to a steady speed and back to a stop. This gives a visual to the concepts positive acceleration, zero acceleration and negative acceleration.

Mary Spaulding, Clearbrook-Gonvick Public School, Clearbrook Minnesota, based on an original activity from Physics Principles and Problems (1995) page 75.

314

Angular Acceleration without Torque?  

ERIC Educational Resources Information Center

|Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.|

Kaufman, Richard D.

2012-01-01

315

Force, mass and acceleration  

Microsoft Academic Search

Force, mass and acceleration are everyday words but often used inaccurately. Force is a physical influence, which when applied to an object causes it to accelerate in the direction from which it was applied. Mass is the amount of matter in an object and is expressed in kilograms. Acceleration is the rate of change of velocity of an object in

Phil Dalrymple; Richard Griffiths

2005-01-01

316

Mechanical Rotary Acceleration Sensor.  

National Technical Information Service (NTIS)

The mechanical rotary acceleration device senses both acceleration and deceleration of a rotating member and responds to control switches or the like to correct the acceleration. The device is used in the field of airlaunched, towed targetry in which a co...

E. J. McQuillen

1965-01-01

317

Heavy ion space charge limits  

Microsoft Academic Search

Modern ultra-high vacuum technology makes it possible to accelerate and store heavy ions in low charge states. Such quasi-neutralized beams give rise to very high space charge limits in conventional charged particle storage rings and transport systems. In addition, the z squared dependence of dE\\/dx gives rise to very short ranges for very high energies. Space charge limits are evaluated

A. W. Maschke

1975-01-01

318

Covariant Uniform Acceleration  

NASA Astrophysics Data System (ADS)

We derive a 4D covariant Relativistic Dynamics Equation. This equation canonically extends the 3D relativistic dynamics equation , where F is the 3D force and p = m0?v is the 3D relativistic momentum. The standard 4D equation is only partially covariant. To achieve full Lorentz covariance, we replace the four-force F by a rank 2 antisymmetric tensor acting on the four-velocity. By taking this tensor to be constant, we obtain a covariant definition of uniformly accelerated motion. This solves a problem of Einstein and Planck. We compute explicit solutions for uniformly accelerated motion. The solutions are divided into four Lorentz-invariant types: null, linear, rotational, and general. For null acceleration, the worldline is cubic in the time. Linear acceleration covariantly extends 1D hyperbolic motion, while rotational acceleration covariantly extends pure rotational motion. We use Generalized Fermi-Walker transport to construct a uniformly accelerated family of inertial frames which are instantaneously comoving to a uniformly accelerated observer. We explain the connection between our approach and that of Mashhoon. We show that our solutions of uniformly accelerated motion have constant acceleration in the comoving frame. Assuming the Weak Hypothesis of Locality, we obtain local spacetime transformations from a uniformly accelerated frame K' to an inertial frame K. The spacetime transformations between two uniformly accelerated frames with the same acceleration are Lorentz. We compute the metric at an arbitrary point of a uniformly accelerated frame. We obtain velocity and acceleration transformations from a uniformly accelerated system K' to an inertial frame K. We introduce the 4D velocity, an adaptation of Horwitz and Piron s notion of "off-shell." We derive the general formula for the time dilation between accelerated clocks. We obtain a formula for the angular velocity of a uniformly accelerated object. Every rest point of K' is uniformly accelerated, and its acceleration is a function of the observer's acceleration and its position. We obtain an interpretation of the Lorentz-Abraham-Dirac equation as an acceleration transformation from K' to K.

Friedman, Yaakov; Scarr, Tzvi

2013-04-01

319

Unlimited Ion Acceleration by Radiation Pressure  

SciTech Connect

The energy of ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region resulting in an increase in the ion energy and in the ion longitudinal velocity. In the relativistic limit, the ions become phase locked with respect to the electromagnetic wave resulting in unlimited ion energy gain.

Bulanov, S. V.; Esirkepov, T. Zh.; Kando, M. [Kansai Photon Science Institute, JAEA, Kizugawa, Kyoto 619-0215 (Japan); Echkina, E. Yu.; Inovenkov, I. N. [CMC, Moscow State University, Moscow 119899 (Russian Federation); Pegoraro, F. [Physics Department, University of Pisa and CNISM, Pisa 56127 (Italy); Korn, G. [Max Plank Institute of Quantum Optics, Garching 85748 (Germany)

2010-04-02

320

Advanced Accelerator Test Facility (AATF) upgrade plan  

SciTech Connect

We have successfully demonstrated the principles of wake-field acceleration using structures (cavity, dielectric) and plasmas as wake-field devices using the AATF at Argonne National Laboratory. Due to the limited driver electron pulse intensity and relative long pulse length, only modest accelerating gradients were observed. In order to study the wake field effects in much greater detail and demonstrate the feasibility of wake-field accelerator for high energy physics, we are considering construction of a laser photocathode injector on the existing 20 MeV Chem-Linac to produce very intense and short electron pulses. 10 refs., 5 figs.

Gai, W.; Ho, C.; Konecny, R.; Mtingwa, S.; Norem, J.; Rosenzweig, J.; Schoessow, P.; Simpson, J.; Cole, B.; Rosing, M.

1989-01-01

321

High brightness electron accelerator  

DOEpatents

A compact high brightness linear accelerator is provided for use, e.g., in a free electron laser. The accelerator has a first plurality of acclerating cavities having end walls with four coupling slots for accelerating electrons to high velocities in the absence of quadrupole fields. A second plurality of cavities receives the high velocity electrons for further acceleration, where each of the second cavities has end walls with two coupling slots for acceleration in the absence of dipole fields. The accelerator also includes a first cavity with an extended length to provide for phase matching the electron beam along the accelerating cavities. A solenoid is provided about the photocathode that emits the electons, where the solenoid is configured to provide a substantially uniform magnetic field over the photocathode surface to minimize emittance of the electons as the electrons enter the first cavity.

Sheffield, Richard L. (Los Alamos, NM); Carlsten, Bruce E. (Los Alamos, NM); Young, Lloyd M. (Los Alamos, NM)

1994-01-01

322

Chronic ozone exposure affects leaf senescence of adult beech trees: a chlorophyll fluorescence approach.  

PubMed

Accelerated leaf senescence is one of the harmful effects of elevated tropospheric ozone concentrations ([O(3)]) on plants. The number of studies dealing with mature forest trees is scarce however. Therefore, five 66-year-old beech trees (Fagus sylvatica L.) have been exposed to twice-ambient (2xambient) [O(3)] levels by means of a free-air canopy O(3) exposure system. During the sixth year of exposure, the hypothesis of accelerated leaf senescence in 2xambient [O(3)] compared with ambient [O(3)] trees was tested for both sun and shade leaves. Chlorophyll (chl) fluorescence was used to assess the photosynthetic quantum yield, and chl fluorescence images were processed to compare functional leaf homogeneity and the proportion of O(3)-injured leaf area (stipples) under ambient and 2xambient [O(3)] regimes. Based on the analysis of chl fluorescence images, sun leaves of both ambient and 2xambient [O(3)] trees had apparently developed typical necrotic O(3) stipples during high O(3) episodes in summer, while accelerated senescence was only observed with sun leaves of 2xambient [O(3)] trees. This latter effect was indicated along with a faster decrease of photosynthetic quantum yield, but without evidence of changes in non-photochemical quenching. Overall, treatment effects were small and varied among trees. Therefore, compared with ambient [O(3)], the consequence of the observed O(3)-induced accelerated leaf senescence for the carbon budget is likely limited. PMID:17150989

Gielen, Birgit; Löw, Markus; Deckmyn, Gaby; Metzger, Ursula; Franck, Fabrice; Heerdt, Christian; Matyssek, Rainer; Valcke, Roland; Ceulemans, Reinhart

2006-12-05

323

The accelerated testing of cements in brines  

SciTech Connect

Cementitious materials may be employed in settings where they face prolonged exposure to Mg-rich brines. This study evaluated the possibility of using high temperatures to accelerate brine-cement reaction rates. Class-H cement coupons were tested in Mg-K-Na-C1- SO{sub 4} brines to 100{degrees}C. MgC1{sub 2}-NaC1 solutions were also employed in a test sequence that extended to 200{degrees}C. It was found that accelerated testing could be used successfully to evaluate the compatability of cementitious materials with such brines.

Krumhansl, J.L.

1993-12-31

324

An introduction to acceleration mechanisms  

SciTech Connect

This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, Acceleration, Plasma Beat Wave Acceleration, Inverse Free Electron Laser Acceleration, Inverse Cerenkov Acceleration, Gravity Acceleration, 2D Linac Acceleration and Conventional Iris Loaded Linac Structure Acceleration. (LSP)

Palmer, R.B.

1987-05-01

325

Retrospective assessment of occupational exposure to whole-body vibration for a case-control study.  

PubMed

Occupational whole-body vibration is often studied as a risk factor for conditions that may arise soon after exposure, but only rarely have studies examined associations with conditions arising long after occupational exposure has ceased. We aimed to develop a method of constructing previous occupational whole-body vibration exposure metrics from self-reported data collected for a case-control study of Parkinson's disease. A detailed job history and exposure interview was administered to 808 residents of British Columbia, Canada (403 people with Parkinson's disease and 405 healthy controls). Participants were prompted to report exposure to whole-body vibrating equipment. We limited the data to exposure reports deemed to be above background exposures and used the whole-body vibration literature (typically reporting on seated vector sum measurements) to assign intensity (acceleration) values to each type of equipment reported. We created four metrics of exposure (duration of exposure, most intense equipment exposure, and two dose metrics combining duration and intensity) and examined their distributions and correlations. We tested the role of age and gender in predicting whole-body vibration exposure. Thirty-six percent of participants had at least one previous occupational exposure to whole-body vibrating equipment. Because less than half of participants reported exposure, all continuous metrics exhibited positively skewed distributions, although the distribution of most intense equipment exposure was more symmetrically distributed among the exposed. The arithmetic mean of duration of exposure among those exposed was 14.0 (standard deviation, SD: 14.2) work years, while the geometric mean was 6.8 (geometric SD, GSD: 4.5). The intensity of the most intense equipment exposure (among the exposed) had an arithmetic mean of 0.9 (SD: 0.3) m·s(-2) and a geometric mean of 0.8 (GSD: 1.4). Male gender and older age were both associated with exposure, although the effect of age was attenuated after adjustment for gender. The methods developed allowed us to create continuous metrics of whole-body vibration retrospectively, displaying useful variance for epidemiologic studies. PMID:22571854

Harris, M Anne; Cripton, Peter A; Teschke, Kay

2012-01-01

326

High temperature experiment for accelerator inertial fusion  

SciTech Connect

The High Temperature Experiment (HTE) is intended to produce temperatures of 50 to 100 eV in solid density targets driven by heavy ion beams from a multiple beam induction linac. The fundamental variables (particle species, energy, number of beamlets, current and pulse length) must be fixed to achieve the temperature at minimum cost, subject to criteria of technical feasibility and relevance to the development of a Fusion Driver. The conceptual design begins with an assumed (radiation-limited) target temperature and uses limitations due to particle range, beamlet perveance, and target disassembly to bound the allowable values of mass number (A) and energy (E). An accelerator model is then applied to determine the minimum length accelerator, which is a guide to total cost. The accelerator model takes into account limits on transportable charge, maximum gradient, core mass per linear meter, and head-to-tail momentum variation within a pulse.

Lee, E.P.

1985-05-01

327

Particle-accelerator decommissioning  

SciTech Connect

Generic considerations involved in decommissioning particle accelerators are examined. There are presently several hundred accelerators operating in the United States that can produce material containing nonnegligible residual radioactivity. Residual radioactivity after final shutdown is generally short-lived induced activity and is localized in hot spots around the beam line. The decommissioning options addressed are mothballing, entombment, dismantlement with interim storage, and dismantlement with disposal. The recycle of components or entire accelerators following dismantlement is a definite possibility and has occurred in the past. Accelerator components can be recycled either immediately at accelerator shutdown or following a period of storage, depending on the nature of induced activation. Considerations of cost, radioactive waste, and radiological health are presented for four prototypic accelerators. Prototypes considered range from small accelerators having minimal amounts of radioactive mmaterial to a very large accelerator having massive components containing nonnegligible amounts of induced activation. Archival information on past decommissionings is presented, and recommendations concerning regulations and accelerator design that will aid in the decommissioning of an accelerator are given.

Opelka, J.H.; Mundis, R.L.; Marmer, G.J.; Peterson, J.M.; Siskind, B.; Kikta, M.J.

1979-12-01

328

Plasma inverse transition acceleration  

SciTech Connect

It can be proved fundamentally from the reciprocity theorem with which the electromagnetism is endowed that corresponding to each spontaneous process of radiation by a charged particle there is an inverse process which defines a unique acceleration mechanism, from Cherenkov radiation to inverse Cherenkov acceleration (ICA) [1], from Smith-Purcell radiation to inverse Smith-Purcell acceleration (ISPA) [2], and from undulator radiation to inverse undulator acceleration (IUA) [3]. There is no exception. Yet, for nearly 30 years after each of the aforementioned inverse processes has been clarified for laser acceleration, inverse transition acceleration (ITA), despite speculation [4], has remained the least understood, and above all, no practical implementation of ITA has been found, until now. Unlike all its counterparts in which phase synchronism is established one way or the other such that a particle can continuously gain energy from an acceleration wave, the ITA to be discussed here, termed plasma inverse transition acceleration (PITA), operates under fundamentally different principle. As a result, the discovery of PITA has been delayed for decades, waiting for a conceptual breakthrough in accelerator physics: the principle of alternating gradient acceleration [5, 6, 7, 8, 9, 10]. In fact, PITA was invented [7, 8] as one of several realizations of the new principle.

Xie, Ming

2001-06-18

329

Accelerated leach test development program  

SciTech Connect

In FY 1989, a draft accelerated leach test for solidified waste was written. Combined test conditions that accelerate leaching were validated through experimental and modeling efforts. A computer program was developed that calculates test results and models leaching mechanisms. This program allows the user to determine if diffusion controls leaching and, if this is the case, to make projections of releases. Leaching mechanisms other than diffusion (diffusion plus source term partitioning and solubility limited leaching) are included in the program is indicators of other processes that may control leaching. Leach test data are presented and modeling results are discussed for laboratory scale waste forms composed of portland cement containing sodium sulfate salt, portland cement containing incinerator ash, and vinyl ester-styrene containing sodium sulfate. 16 refs., 38 figs., 5 tabs.

Fuhrmann, M.; Pietrzak, R.F.; Heiser, J.; Franz, E.M.; Colombo, P.

1990-11-01

330

Ion Acceleration During Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

We explore the mechanism for ion acceleration during magnetic reconnection to understand the energetic particle spectra produced during flares and in the solar wind. Reconnection driven ion acceleration is initiated as particles move from upstream into the Alfvenic exhaust. In the case of a weak guide field, protons and higher mass particles behave like pickup particles in that they abruptly cross a narrow boundary layer and find themselves in a region of Alfvenic outflow. Their motion then mimics that of a classic pickup ion, gaining an Alfvenic ExB flow in the jet and a thermal speed close to the Alfven speed. In the case of a strong guide field particle acceleration is strongly enhanced for ions with high mass-to-charge (m/q) ratio since these particles act as pick-up particles while small m/q particles are adiabatic. Once ions become super-Aflvenic their acceleration is, like electrons, dominated by Fermi reflection during island contraction and their energy increases until it is limited by firehose marginal stability. The ion distribution function for super-Alfvenic ions then takes the form of a v-5 distribution. During reconnection in a multi-island environment, as in flares, strong enhancements in high m/q ions are expected. This picture is consistent with several observations related to flare and local solar wind ion acceleration: (1) the ubiquitous observations of energy proportional to mass; (2) strong enhancements in high m/q ions during impulsive flares; and (3) the temperature increments of solar wind exhausts.

Drake, J. F.; Swisdak, M.; Phan, T. D.; Cassak, P. A.; Shay, M. A.; Lepri, S. T.; Quataert, E.; Lin, R. P.; Zurbuchen, T. H.

2008-12-01

331

Actinides, accelerators and erosion  

NASA Astrophysics Data System (ADS)

Fallout isotopes can be used as artificial tracers of soil erosion and sediment accumulation. The most commonly used isotope to date has been 137Cs. Concentrations of 137Cs are, however, significantly lower in the Southern Hemisphere, and furthermore have now declined to 35% of original values due to radioactive decay. As a consequence the future utility of 137Cs is limited in Australia, with many erosion applications becoming untenable within the next 20 years, and there is a need to replace it with another tracer. Plutonium could fill this role, and has the advantages that there were six times as many atoms of Pu as of 137Cs in fallout, and any loss to decay has been negligible due to the long half-lives of the plutonium isotopes. Uranium-236 is another long-lived fallout isotope with significant potential for exploitation as a tracer of soil and sediment movement. Uranium is expected to be more mobile in soils than plutonium (or caesium), and hence the 236U/Pu ratio will vary with soil depth, and so could provide an independent measure of the amount of soil loss. In this paper we discuss accelerator based ultra-sensitive measurements of plutonium and 236U isotopes and their advantages over 137Cs as tracers of soil erosion and sediment movement.

Tims, S. G.; Fifield, L. K.

2012-10-01

332

Supernova / Acceleration Probe: Instrumentation  

NASA Astrophysics Data System (ADS)

The Supernova / Acceleration Probe (SNAP) is a space experiment to measure the cosmological parameters and investigate the properties of the dark energy. The SNAP science goals require the control of measurement systematics using high resolution, high signal-to-noise photometric and spectrocopic observations. These science goals drive the design requirements for SNAP instrumentation. We describe an instrument suite which is optimized to meet these stringent requirements. The baseline optic is a diffraction limited, f/10, three-mirror, anastigmatic, 2-meter class telescope with a plate scale of 0.1 arcsec/pixel. The optical imager is a wide field, one square degree, billion pixel CCD mosaic. A high-resolution, near-IR camera consists of a HgCdTe array, with a FOV of 10 square arcminutes, covering the wavelength region from 1 to 1.7 microns. An optical/NIR multi-arm spectrograph system with resolution approximately R=200, comprises the third science instrument. Other instruments include a star tracker able to guide with a stability of within 0.03 arcsec. This project is funded in part by the US DOE and the NSF.

Deustua, S.; Aldering, G.; Astier, P.; Baden, A.; Bebek, C.; Bergstrom, L.; Curtis, D.; Edwards, W.; Ellis, R.; Fruchter, A.; Frye, B.; Genat, J. F.; Goldhaber, G.; Goobar, A.; Goodman, J.; Graham, J.; Hardin, D.; Harris, S.; Harvey, P.; Heetderks, H.; Holland, S.; Hook, I.; Huterer, D.; Kasen, D.; Kim, A.; Knop, R.; Lafever, R.; Lampton, M.; Levi, M.; Levy, J.-M.; Lidman, C.; Lin, R.; Loken, S.; Metzger, M.; Mourao, A.; Nugent, P.; Pain, R.; Pankow, D.; Pennypacker, C.; Perlmutter, S.; Rich, J.; Robinson, K.; Schamahneche, K.; Spadafora, A.; Smoot, G.; Sullivan, G.; SNAP Collaboration

2000-12-01

333

Staged laser plasma accelerators  

NASA Astrophysics Data System (ADS)

We present current results on staged electron acceleration in the LOASIS program at the Lawrence Berkeley National Laboratory. The goal is to experimentally demonstrate laser driven electron acceleration in two stages, where each stage is driven by a separate laser pulse. This technology could provide the key to built compact laser driven accelerators which could potentially reach up to TeV in electron energy.

Sokollik, Thomas; Shiraishi, Satomi; Shaw, Brian; Gonsalves, Antony; Nakamura, Kei; van Tilborg, Jeroen; Esarey, Eric; Schroeder, Carl B.; Benedetti, Carlo; Toth, Csaba; Leemans, Wim

2012-12-01

334

Linear induction accelerator  

SciTech Connect

A linear induction accelerator of charged particles, containing inductors and an acceleration circuit, characterized by the fact that, for the purpose of increasing the power of the accelerator, each inductor is made in the form of a toroidal line with distributed parameters, from one end of which in the gap of the line a ring commutator is included, and from the other end of the ine a resistor is hooked up, is described.

Bosamykin, V.S.; Pavlovskiy, A.I.

1984-03-01

335

Linear inductive accelerator  

SciTech Connect

A proposed accelerator, differing from existing ones in that it is loaded through a capacitor on a solenoid which is uniformly distributed throughout the accelerating system and connected to an independent electrical current source, is discussed. The design of the system makes it possible to improve the uniformity of the electrical field and increase the longitudinal focusing magnetic field. This is especially important for high-current accelerators.

Bosamykin, V.S.; Gerasimov, A.I.; Pavlovskiy, A.I.

1983-11-01

336

ACCELERATION RESPONSIVE SWITCH  

DOEpatents

An acceleration-responsive device with dual channel capabilities whereby a first circuit is actuated upon attainment of a predetermined maximum acceleration level and when the acceleration drops to a predetermined minimum acceleriltion level another circuit is actuated is described. A fluid-damped sensing mass slidably mounted in a relatively frictionless manner on a shaft through the intermediation of a ball bushing and biased by an adjustable compression spring provides inertially operated means for actuating the circuits. (AEC)

Chabrek, A.F.; Maxwell, R.L.

1963-07-01

337

High-intensity accelerators  

SciTech Connect

The design of high-intensity accelerators is described, using examples of machines being built at the Los Alamos National Laboratory. The major design problem with these accelerators is associated with control of beam loss when accelerator intensity is increased. Beam dynamics, beam loss, and the radio-frequency quadrupole structure are discussed in the first part of the chapter followed by an explanation of plans to achieve high-intensity operation in three projects: the Fusion Material Irradiation Tests (a joint effort with the Hanford Development Laboratory in Richland, Washington), the Proton Storage Ring (an addition to the LAMPF accelerator), and the Racetrack Microtron Project (with the National Bureau of Standards).

Knapp, E.A.

1981-01-01

338

Cumulative Aspects of Repeated HSG Exposure.  

National Technical Information Service (NTIS)

A system is described for acceleration treatment of domestic fowl. A reasonable end point for acceleration tolerance is provided by a bradycardia that occurs fairly close to the lethal limit. In a group of 61 male Rhode Island Red chickens exposed to +6 G...

A. H. Smith E. A. Rhode W. L. Spangler

1979-01-01

339

EXPOSURE ASSESSMENT: INPUT INTO RISK ASSESSMENT  

EPA Science Inventory

The validity of a risk assessment can be no better than that of the exposure assessment upon which it is based. he general paucity of relevant exposure data, combined with the limited appreciation by most risk assessors of the critical dimensions and metrics of exposure, often le...

340

Acceleration of polarized protons in circular accelerators  

SciTech Connect

The theory of depolarization in circular accelerators is presented. The spin equation is first expressed in terms of the particle orbit and then converted to the equivalent spinor equation. The spinor equation is then solved for three different situations: (1) a beam on a flat top near a resonance, (2) uniform acceleration through an isolated resonance, and (3) a model of a fast resonance jump. Finally, the depolarization coefficient, epsilon, is calculated in terms of properties of the particle orbit and the results are applied to a calculation of depolarization in the AGS.

Courant, E.D.; Ruth, R.D.

1980-09-12

341

Octupole focusing in transport and acceleration systems  

SciTech Connect

The radio-frequency quadrupole (RFQ) linac is capable of accelerating high-current, low-velocity ion beams. In accelerator systems comprising an RFQ and higher velocity accelerating structures, the current bottleneck still typically occurs within the RFQ. This limiting current is quite high in most cases, but linacs with even higher currents may be required in the future. We have begun a study of higher multipole systems to determine their capability for focusing and accelerating very high currents. We have chosen first to examine a radio-frequency octupole (RFO) transport system, and have developed a smooth-approximation analytical description that includes the conditions for input radial matching of a zero space-charge beam. Further, we have constructed a multiparticle beam-dynamics simulation program that accepts the low-current matched beam and gradually increases the beam current as it is transported. This results in a matched high-current beam, and the procedure can be used to determine the saturation-current limit of a periodic octupole system. As expected, at high currents the beam develops a hollow radial distribution that reduces the space-charge defocusing; initial results show that high currents can be transported. For acceleration, we have formulated the design parameters for a section of RFO linac, including the potential function, acceleration, and focusing efficiencies, and the geometry of the radially modulated pole tips.

Crandall, K.R.; Pabst, M.; Stokes, R.H.; Wangler, T.P.

1981-01-01

342

Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

Laser-driven acceleration holds great promise for significantly improving accelerating gradient. However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals---structures whose electromagnetic properties are spatially periodic---can meet these requirements. We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide. We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter. We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.

Cowan, Benjamin M.

2007-08-22

343

Rf cavity primer for cyclic proton accelerators  

SciTech Connect

The purpose of this note is to describe the electrical and mechanical properites of particle accelerator rf cavities in a manner which will be useful to physics and engineering graduates entering the accelerator field. The discussion will be limited to proton (or antiproton) synchrotron accelerators or storage rings operating roughly in the range of 20 to 200 MHz. The very high gradient, fixed frequency UHF or microwave devices appropriate for electron machines and the somewhat lower frequency and broader bandwidth devices required for heavy ion accelerators are discussed extensively in other papers in this series. While it is common pratice to employ field calculation programs such as SUPERFISH, URMEL, or MAFIA as design aids in the development of rf cavities, we attempt here to elucidate various of the design parameters commonly dealt with in proton machines through the use of simple standing wave coaxial resonator expressions. In so doing, we treat only standing wave structures. Although low-impedance, moderately broad pass-band travelling wave accelerating systems are used in the CERN SPS, such systems are more commonly found in linacs, and they have not been used widely in large cyclic accelerators. Two appendices providing useful supporting material regarding relativistic particle dynamics and synchrotron motion in cyclic accelerators are added to supplement the text.

Griffin, J.E.

1988-04-01

344

DESIGN CRITERIA OF A PROTON FFAG ACCELERATOR.  

SciTech Connect

There are two major issues that are to be confronted in the design of a Fixed-Field Alternating-Gradient (FFAG) accelerator, namely: (1) the stability of motion over the large momentum range needed for the beam acceleration, and (2) the compactness of the trajectories over the same momentum range to limit the dimensions of the magnets. There are a numbers of rules that need to be followed to resolve these issues. In particular, the magnet arrangement in the accelerator lattice and the distribution of the bending and focusing fields are to be set properly in accordance with these rules. In this report they describe four of these rules that ought to be applied for the optimum design of a FFAG accelerator, especially in the case of proton beams.

RUGGIERO, A.G.

2004-10-13

345

Laser-plasma accelerator: status and perspectives.  

PubMed

Laser-plasma accelerators deliver high-charge quasi-monoenergetic electron beams with properties of interest for many applications. Their angular divergence, limited to a few mrad, permits one to generate a small gamma ray source for dense matter radiography, whereas their duration (few tens of fs) permits studies of major importance in the context of fast chemistry for example. In addition, injecting these electron beams into a longer plasma wave structure will extend their energy to the GeV range. A GeV laser-based accelerator scheme is presented; it consists of the acceleration of this electron beam into relativistic plasma waves driven by a laser. This compact approach (centimetres scale for the plasma, and tens of meters for the whole facility) will allow a miniaturization and cost reduction of future accelerators and derived X-ray free electron laser (XFEL) sources. PMID:16483951

Malka, V; Faure, J; Glinec, Y; Lifschitz, A F

2006-03-15

346

Plasma beat-wave accelerator  

SciTech Connect

We perform an analytic study of some quantities relevant to the plasma beat-wave accelerator (PBWA) concept. We obtain analytic expressions for the plasma frequency, longitudinal electron velocity, plasma density and longitudinal plasma electric field of a nonlinear longitudinal electron plasma oscillation with amplitude less than the wave-breaking limit and phase velocity approaching the speed of light. We also estimate the luminosity of a single-pass e/sup +/e/sup -/ linear PBWA collider assuming the energy and collision beamstrahlung are fixed parameters.

Noble, R.J.

1983-06-01

347

Accelerating the Development of Hardware Accelerators  

Microsoft Academic Search

ASC (1), A Stream Compiler, is designed to enable rapid development of hardware accelerators while still producing results that match hand-crafted equivalents. An ASC pro- gram represents a dataflow system which can be seen as a stream; to avoid the difficulties often associated with be- havioural synthesis, ASC allows direct implementation of a hardware design based on the programmer's input.

Lee W. Howes; Oliver Pell; Oskar Mencer; Olav Beckmann

348

Accelerator Toolbox for MATLAB.  

National Technical Information Service (NTIS)

This paper introduces Accelerator Toolbox (AT) - a collection of tools to model particle accelerators and beam transport lines in the MATLAB environment. At SSRL, it has become the modeling code of choice for the ongoing design and future operation of the...

A. Terebilo

2001-01-01

349

Accelerators for energy production  

NASA Astrophysics Data System (ADS)

A tremendous progress of accelerators for these several decades, has been motivated mainly by the research on subnuclear physics. The culmination in high energy accelerators might be SSC, 20 TeV collider in USA, probably the ultimate accelerator being built with the conventional principle. The technology cultivated and integrated for the accelerator development, can now stably offer the high power beam which could be used for the energy problems. The Inertial Confinement Fusion (ICF) with high current, 10 kA and short pulse, 20 ns heavy ion beam (HIB) of mass number approximately 200, would be the most promising application of accelerators for energy production. In this scenario, the fuel containing D-T mixture, will be compressed to the high temperature, approximately 10 keV and to the high density state, approximately 1000 times the solid density with the pressure of ablative plasma or thermal X ray produced by bombarding of high power HIB. The efficiency, beam power/electric power for accelerator, and the repetition rate of HIB accelerators could be most suitable for the energy production. In the present paper, the outline of HIB ICF (HIF) is presented emphasizing the key issues of high current heavy ion accelerator system.

Katayama, Takeshi

1993-11-01

350

KEK digital accelerator  

NASA Astrophysics Data System (ADS)

The High Energy Accelerator Research Organization KEK digital accelerator (KEK-DA) is a renovation of the KEK 500 MeV booster proton synchrotron, which was shut down in 2006. The existing 40 MeV drift tube linac and rf cavities have been replaced by an electron cyclotron resonance (ECR) ion source embedded in a 200 kV high-voltage terminal and induction acceleration cells, respectively. A DA is, in principle, capable of accelerating any species of ion in all possible charge states. The KEK-DA is characterized by specific accelerator components such as a permanent magnet X-band ECR ion source, a low-energy transport line, an electrostatic injection kicker, an extraction septum magnet operated in air, combined-function main magnets, and an induction acceleration system. The induction acceleration method, integrating modern pulse power technology and state-of-art digital control, is crucial for the rapid-cycle KEK-DA. The key issues of beam dynamics associated with low-energy injection of heavy ions are beam loss caused by electron capture and stripping as results of the interaction with residual gas molecules and the closed orbit distortion resulting from relatively high remanent fields in the bending magnets. Attractive applications of this accelerator in materials and biological sciences are discussed.

Iwashita, T.; Adachi, T.; Takayama, K.; Leo, K. W.; Arai, T.; Arakida, Y.; Hashimoto, M.; Kadokura, E.; Kawai, M.; Kawakubo, T.; Kubo, Tomio; Koyama, K.; Nakanishi, H.; Okazaki, K.; Okamura, K.; Someya, H.; Takagi, A.; Tokuchi, A.; Wake, M.

2011-07-01

351

Review of Accelerator Alignment  

Microsoft Academic Search

SUMMARY The history of twentieth century science and technology is intimately tied to the development of particle accelerators and the discoveries made using them. Today the breadth of science concerned by, and studied using particle accelerators is truly staggering. It ranges from attempts to understand the origin of our universe and what constitutes matter and radiation; to questions concerning the

David MARTIN

2010-01-01

352

Neutrino physics at accelerators  

Microsoft Academic Search

Present and future neutrino experiments at accelerators are mainly concerned with understanding the neutrino oscillation phenomenon and its implications. Here a brief account of neutrino oscillations is given together with a description of the supporting data. Some current and planned accelerator neutrino experiments are also explained. Neutrinos are particles that interact only weakly and this gives them a somewhat special

Enrique Fernandez

353

Twisted waveguide accelerating structure..  

National Technical Information Service (NTIS)

A hollow waveguide with a uniform cross section may be used for accelerating charged particles if the phase velocity of an accelerating mode is equal to or less than the fiee space speed of light. Regular straight hollow waveguides have phase velocities o...

Y. W. Kang

2000-01-01

354

Accelerators Beyond The Tevatron?  

SciTech Connect

Following the successful operation of the Fermilab superconducting accelerator three new higher energy accelerators were planned. They were the UNK in the Soviet Union, the LHC in Europe, and the SSC in the United States. All were expected to start producing physics about 1995. They did not. Why?.

Lach, Joseph [Fermi National Accelerator Laboratory, P.O Box 500, Batavia Illinois (United States)

2010-07-29

355

Acceleration of Gravity 2  

NSDL National Science Digital Library

This lab is between a Level 2 and Level 3 inquiry activity in that it should be assigned after students understand acceleration but before they learn about the acceleration gravity. Because there are many sources of error when using a pendulum, students c

Horton, Michael

2009-05-30

356

Exploring acceleration through vectors  

NSDL National Science Digital Library

This in class worksheet is designed to get students to think about and manipulate different accelerations in their head. Students work together with written descriptions of velocity and acceleration and draw the vectors in part one, and then turn that around in part two where they write descriptions of a car's motion based on the vector pictures they are given.

357

Diagnostics for induction accelerators  

SciTech Connect

The induction accelerator was conceived by N. C. Christofilos and first realized as the Astron accelerator that operated at LLNL from the early 1960`s to the end of 1975. This accelerator generated electron beams at energies near 6 MeV with typical currents of 600 Amperes in 400 ns pulses. The Advanced Test Accelerator (ATA) built at Livermore`s Site 300 produced 10,000 Ampere beams with pulse widths of 70 ns at energies approaching 50 MeV. Several other electron and ion induction accelerators have been fabricated at LLNL and LBNL. This paper reviews the principal diagnostics developed through efforts by scientists at both laboratories for measuring the current, position, energy, and emittance of beams generated by these high current, short pulse accelerators. Many of these diagnostics are closely related to those developed for other accelerators. However, the very fast and intense current pulses often require special diagnostic techniques and considerations. The physics and design of the more unique diagnostics developed for electron induction accelerators are presented and discussed in detail.

Fessenden, T.J.

1996-04-01

358

Mercury Exposure and Child Development Outcomes  

Microsoft Academic Search

Mercury is ubiquitous in the global envi- ronment, ensuring universal exposure. Some forms of mercury are especially neurotoxic, including clinical signs at high doses. However, typical human exposures occur at low to moderate doses. Only limited data about neurotoxicity at low doses are available, and scientists differ in their interpretation. Dose-response data on neu- rodevelopment are particularly limited. Despite or

Philip W. Davidson; Gary J. Myers; Bernard Weiss

2009-01-01

359

Falsifying paradigms for cosmic acceleration  

SciTech Connect

Consistency relations between growth of structure and expansion history observables exist for any physical explanation of cosmic acceleration, be it a cosmological constant, scalar field quintessence, or a general component of dark energy that is smooth relative to dark matter on small scales. The high-quality supernova sample anticipated from an experiment like the SuperNova/Acceleration Probe and cosmic microwave background data expected from Planck thus make strong predictions for growth and expansion observables that additional observations can test and potentially falsify. We perform a Markov chain Monte Carlo likelihood exploration of the strength of these consistency relations based on a complete parametrization of dark energy behavior by principal components. For {lambda}CDM, future supernova and cosmic microwave background data make percent level predictions for growth and expansion observables. For quintessence, many of the predictions are still at a level of a few percent with most of the additional freedom coming from curvature and early dark energy. While such freedom is limited for quintessence where phantom equations of state are forbidden, it is larger in the smooth dark energy class. Nevertheless, even in this general class predictions relating growth measurements at different redshifts remain robust, although predictions for the instantaneous growth rate do not. Finally, if observations falsify the whole smooth dark energy class, new paradigms for cosmic acceleration such as modified gravity or interacting dark matter and dark energy would be required.

Mortonson, Michael J.; Hu, Wayne; Huterer, Dragan [Kavli Institute for Cosmological Physics and Department of Physics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States); Kavli Institute for Cosmological Physics and Department of Astronomy and Astrophysics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States); Department of Physics, University of Michigan, 450 Church Street Ann Arbor, Michigan 48109-1040 (United States)

2009-01-15

360

Open accelerating structures  

SciTech Connect

An ''Open'' Accelerating Structure must first perform the mode matching function of any accelerating structure, i.e., it must couple an incoming free field to an accelerating mode. The simplest open periodic structure that can be considered is a grating. There has been an attempt to employ an inverse Purcell effect by illuminating a grating from directly above with plane parallel light and passing the particles over the surface of the grating at right angles to the lines. Unfortunately, it has been shown by the Lawson theorem that these geometries fail to accelerate relativistic particles. This paper will restate Lawson's theorem but show that it applies only to the simple two-dimensional situation. It is shown that accelerating fields above grating can be made to fall off exponentially from that surface. Several structures are examined that deal with the problem of fields spreading over the whole grating surface.

Palmer, R.B.

1986-12-01

361

Tritium Exposure Reconstruction Using Tree Rings at Lawrence Berkeley National Laboratory  

NASA Astrophysics Data System (ADS)

There are numerous instances where historical exposures to contaminants can determine future health impacts, but limited means exist to reconstruct those exposures from current measurements and models. The National Tritium Labeling Facility at Lawrence Berkeley National Laboratory (LBNL) has released tritiated water into the atmosphere through an adjacent stack since 1969. Some members of the surrounding community are concerned about potential health effects from the emissions and have questioned the accuracy and thoroughness of reported historical release quantities and environmental monitoring. A grove of Eucalyptus globulus surround the emission stack and were used to reconstruct historical exposure levels. Previous studies have demonstrated that plants can be reliably used as passive monitors for tritiated water, as well as many other contaminants. Because trees can sequester tritium into wood during photosynthesis, a tree provides a temporal variation of exposure at least on an annual basis. Milligram-sized samples of wood from cores were measured for carbon-14 and tritium using accelerator mass spectrometry. The carbon-14 measurements were matched with bomb curve levels of carbon-14 to independently assess the age of the wood used for organically bound tritium measurements. The tritium exposure reconstruction was consistent with annual exposure monitoring and release quantities reported by LBNL over the last 30 years. Because this location has an episodic release pattern and complex topographic and meteorological variation, the historical assessment from these environmental measurements is likely to have less uncertainty than mathematical modeling efforts.

Love, A. H.; Hunt, J. R.; Knezovich, J. P.

2002-12-01

362

Energy sweep compensation of induction accelerators  

SciTech Connect

The ETA-II linear induction accelerator (LIA) is designed to drive a microwave free electron laser (FEL). Beam energy sweep must be limited to {plus minus}1% for 50 ns to limit beam corkscrew motion and ensure high power FEL output over the full duration of the beam flattop. To achieve this energy sweep requirement, we have implemented a pulse distribution system and are planning implementation of a tapered pulse forming line (PFL) in the pulse generators driving acceleration gaps. The pulse distribution system assures proper phasing of the high voltage pulse to the electron beam. Additionally, cell-to-cell coupling of beam induced transients is reduced. The tapered PFL compensates for accelerator cell and loading nonlinearities. Circuit simulations show good agreement with preliminary data and predict the required energy sweep requirement can be met.

Sampayan, S.E.; Caporaso, G.J.; Chen, Y-J; Decker, T.A.; Turner, W.C.

1990-09-12

363

Accelerated test methods to determine the long-term behavior of FRP composite structures: environmental effects  

Microsoft Academic Search

Technical literature on the subject of environmental exposure effects related to determining accelerated test methods for the prediction of long-term performance of FRP composite materials for highway structural applications is reviewed in this paper. Effects of environmental exposure of a chemical and a thermal nature on fiber-reinforced polymer (FRP) composites are considered. Such exposures include temperature, moisture and chemicals in

L. C. Bank; T. R. Gentry; A. Barkatt

1995-01-01

364

Multifractal statistics of Lagrangian velocity and acceleration in turbulence.  

PubMed

The statistical properties of velocity and acceleration fields along the trajectories of fluid particles transported by a fully developed turbulent flow are investigated by means of high resolution direct numerical simulations. We present results for Lagrangian velocity structure functions, the acceleration probability density function, and the acceleration variance conditioned on the instantaneous velocity. These are compared with predictions of the multifractal formalism, and its merits and limitations are discussed. PMID:15323634

Biferale, L; Boffetta, G; Celani, A; Devenish, B J; Lanotte, A; Toschi, F

2004-08-04

365

The Limits of Quintessence  

SciTech Connect

We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase-plane of w and w', the dark energy equation-of-state and its time-derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order \\sigma(w')\\approx (1+w), define firm targets for observational tests of the physics of dark energy.

Caldwell, R.R.; Linder, Eric V.

2005-05-24

366

Accelerating advanced mri reconstructions on gpus  

Microsoft Academic Search

Computational acceleration on graphics processing units (GPUs) can make advanced magnetic resonance imaging (MRI) reconstruction algorithms attractive in clinical settings, thereby improving the quality of MR images across a broad spectrum of applications. At present, MR imaging is often limited by high noise levels, significant imaging artifacts, and\\/or long data acquisition (scan) times. Advanced image reconstruction algorithms can mitigate these

Samuel S. Stone; Justin P. Haldar; Stephanie C. Tsao; Wen-mei W. Hwu; Zhi-pei Liang; Bradley P. Sutton

2008-01-01

367

Evolutionary optimization methods for accelerator design  

Microsoft Academic Search

Many problems from the fields of accelerator physics and beam theory can be formulated as optimization problems and, as such, solved using optimization methods. Despite growing efficiency of the optimization methods, the adoption of modern optimization techniques in these fields is rather limited. Evolutionary Algorithms (EAs) form a relatively new and actively developed optimization methods family. They possess many attractive

Alexey A. Poklonskiy

2009-01-01

368

Newton's Laws Problem: Acceleration and Gravity  

NSDL National Science Digital Library

A 10-kg mass is attached via a pulley to another variable mass m (position is in meters and time is in seconds). You can test the limits of the formula for the acceleration of an Atwood's machine by changing the ratio of the masses.

Christian, Wolfgang; Belloni, Mario

2006-01-21

369

Large electrostatic accelerators  

SciTech Connect

The increasing importance of energetic heavy ion beams in the study of atomic physics, nuclear physics, and materials science has partially or wholly motivated the construction of a new generation of large electrostatic accelerators designed to operate at terminal potentials of 20 MV or above. In this paper, the author briefly discusses the status of these new accelerators and also discusses several recent technological advances which may be expected to further improve their performance. The paper is divided into four parts: (1) a discussion of the motivation for the construction of large electrostatic accelerators, (2) a description and discussion of several large electrostatic accelerators which have been recently completed or are under construction, (3) a description of several recent innovations which may be expected to improve the performance of large electrostatic accelerators in the future, and (4) a description of an innovative new large electrostatic accelerator whose construction is scheduled to begin next year. Due to time and space constraints, discussion is restricted to consideration of only tandem accelerators.

Jones, C.M.

1984-01-01

370

Measuring exposures to glycol ethers.  

PubMed Central

In 1981, NIOSH began investigating the potential reproductive health effects resulting from exposures to a class of organic solvents known generically as glycol ethers (GE). This research was begun as a result of the NIOSH criteria document development program which revealed little data available on the health effects of glycol ether exposure. Toxicologic research was begun by NIOSH and other researchers which suggested substantial reproductive effects in animals. These animal data motivated a study of human exposures in the occupational setting. In 1981 and 1982 NIOSH conducted several walk-through surveys which included preliminary measurements of exposures in a variety of industries including painting trades, coal mining, production blending and distribution facilities, aircraft fueling, and communications equipment repair facilities. The human exposure data from these surveys is summarized in this paper with most results well below 1 parts per million (ppm) and only a few values approaching 10 ppm. Blood samples were collected at one site resulting in GE concentrations below the limit of detection. Exposures to airborne glycol ethers, in the industries investigated during the collection of this data, revealed several problems in reliably sampling GE at low concentrations. It became apparent, from the data and observations of work practices, that air monitoring alone provided an inadequate index of GE exposure. Further field studies of exposure to GE are anticipated, pending location of additional groups of exposed workers and development of more reliable methods for characterizing exposure, especially biological monitoring.

Clapp, D E; Zaebst, D D; Herrick, R F

1984-01-01

371

Measuring exposures to glycol ethers.  

PubMed

In 1981, NIOSH began investigating the potential reproductive health effects resulting from exposures to a class of organic solvents known generically as glycol ethers (GE). This research was begun as a result of the NIOSH criteria document development program which revealed little data available on the health effects of glycol ether exposure. Toxicologic research was begun by NIOSH and other researchers which suggested substantial reproductive effects in animals. These animal data motivated a study of human exposures in the occupational setting. In 1981 and 1982 NIOSH conducted several walk-through surveys which included preliminary measurements of exposures in a variety of industries including painting trades, coal mining, production blending and distribution facilities, aircraft fueling, and communications equipment repair facilities. The human exposure data from these surveys is summarized in this paper with most results well below 1 parts per million (ppm) and only a few values approaching 10 ppm. Blood samples were collected at one site resulting in GE concentrations below the limit of detection. Exposures to airborne glycol ethers, in the industries investigated during the collection of this data, revealed several problems in reliably sampling GE at low concentrations. It became apparent, from the data and observations of work practices, that air monitoring alone provided an inadequate index of GE exposure. Further field studies of exposure to GE are anticipated, pending location of additional groups of exposed workers and development of more reliable methods for characterizing exposure, especially biological monitoring. PMID:6499824

Clapp, D E; Zaebst, D D; Herrick, R F

1984-08-01

372

Neck Forces and Moments and Head Accelerations in Side Impact  

Microsoft Academic Search

Objectives: Although side-impact sled studies have investigated chest, abdomen, and pelvic injury mechanics, determination of head accelerations and the associated neck forces and moments is very limited. The purpose of the present study was therefore to determine the temporal forces and moments at the upper neck region and head angular accelerations and angular velocities using postmortem human subjects (PMHS).Methods: Anthropometric

Narayan Yoganandan; Frank A. Pintar; Dennis J. Maiman; Mat Philippens; Jac Wismans

2009-01-01

373

Does antimatter fall with the same acceleration as ordinary matter  

Microsoft Academic Search

Equivalence-principle experiments with ordinary matter probe the gravivector acceleration of antimatter in the same way as do direct measurements of antimatter in free fall and set stringent upper limits on the gravivector acceleration of antimatter predicted by certain quantum-gravity models.

E. G. Adelberger; B. R. Heckel; C. W. Stubbs; Y. Su

1991-01-01

374

Exposure chamber  

DOEpatents

An exposure chamber includes an imperforate casing having a fluid inlet at the top and an outlet at the bottom. A single vertical series of imperforate trays is provided. Each tray is spaced on all sides from the chamber walls. Baffles adjacent some of the trays restrict and direct the flow to give partial flow back and forth across the chambers and downward flow past the lowermost pan adjacent a central plane of the chamber.

Moss, Owen R. (Kennewick, WA); Briant, James K. (Pasco, WA)

1983-01-01

375

Dogbone geometry for recirculating accelerators.  

National Technical Information Service (NTIS)

Most scenarios for accelerating muons require recirculating acceleration. A racetrack shape for the accelerator requires particles with lower energy in early passes to traverse almost the same length of arc as particles with the highest energy. This extra...

S. Berg Johnstone Summers

2001-01-01

376

Twisted waveguide accelerating structure.  

SciTech Connect

A hollow waveguide with a uniform cross section may be used for accelerating charged particles if the phase velocity of an accelerating mode is equal to or less than the free space speed of light. Regular straight hollow waveguides have phase velocities of propagating electromagnetic waves greater than the free-space speed of light. if the waveguide is twisted, the phase velocities of the waveguide modes become slower. The twisted waveguide structure has been modeled and computer simulated in 3-D electromagnetic solvers to show the slow-wave properties for the accelerating mode.

Kang, Y. W.

2000-08-15

377

Advanced Accelerator Concepts  

NASA Astrophysics Data System (ADS)

Current particle accelerators rely on conventional or superconducting radio frequency cavities to accelerate beams of protons or electrons for nuclear and particle research and for medical and materials science studies. New methods for achieving larger accelerating gradients have been proposed and are being studied. These include the use of high power lasers, laser driven plasmas, wake fields generated by intense low energy beams, and millimeter wavelength EM structures. The studies to date, and the prospects for practical applications of these new ideas will be discussed.

Siemann, Robert

1998-04-01

378

Diagnostics for advanced laser acceleration experiments  

SciTech Connect

The first proposal for plasma based accelerators was suggested by 1979 by Tajima and Dawson. Since then there has been a tremendous progress both theoretically and experimentally. The theoretical progress is particularly due to the growing interest in the subject and to the development of more accurate numerical codes for the plasma simulations (especially particle-in-cell codes). The experimental progress follows from the development of multi-terawatt laser systems based on the chirped-pulse amplification technique. These efforts have produced results in several experiments world-wide, with the detection of accelerated electrons of tens of MeV. The peculiarity of these advanced accelerators is their ability to sustain extremely large acceleration gradients. In the conventional radio frequency linear accelerators (RF linacs) the acceleration gradients are limited roughly to 100 MV/m; this is partially due to breakdown which occurs on the walls of the structure. The electrical breakdown is originated by the emission of the electrons from the walls of the cavity. The electrons cause an avalanche breakdown when they reach other metal parts of the RF linacs structure.

Misuri, Alessio

2002-06-01

379

Acceleration cueing simulation device  

US Patent & Trademark Office Database

An acceleration cueing simulation device is disclosed for applying sustai, as well as dynamic, acceleration forces to a trainee pilot as he operates an aircraft simulator. The acceleration cueing device comprises a pair of Helmholtz coils for generating a uniform magnetic field; an aircraft control device for generating a control data signal which is responsive to simulated flight maneuvers performed by the trainee pilot; and a computer system for producing a plurality of digital logic signals which are in response to the control data signal. The plurality of digital logic signals, when converted to analog signals, will energize a plurality of coils which are embedded in a suit and a helmet worn by the trainee pilot. When the trainee pilot is within the magnetic field generated by the Helmholtz coils, the coils embedded within the suit and the helmet provide a plurality of simulated acceleration forces which are exerted upon the trainee pilot.

1981-01-13

380

Far field acceleration.  

National Technical Information Service (NTIS)

Far fields are propagating electromagnetic waves far from their source, boundary surfaces, and free charges. The general principles governing the acceleration of charged particles by far fields are reviewed. A survey of proposed field configurations is gi...

R. C. Fernow

1995-01-01

381

Accelerated testing of batteries.  

National Technical Information Service (NTIS)

Three methods of evaluating accelerated battery test data are described. Criteria for each method are used to determine the minimum test matrix required for accurate predictions. Other test methods involving high current discharge and real time techniques...

S. C. Levy P. Bro

1992-01-01

382

Non-accelerator experiments  

SciTech Connect

This report discusses several topics which can be investigated without the use of accelerators. Topics covered are: (1) proton decay, (2) atmospheric neutrinos, (3) neutrino detection, (4) muons from Cygnus X-3, and (5) the double-beta decay.

Goldhaber, M.

1986-01-01

383

Acceleration Recorder Device.  

National Technical Information Service (NTIS)

The patent application describes a device for use in measuring peak acceleration (g) levels experienced by munitions during rough handling, ballistic launching or at terminal impact. The device is a self-contained mechanical concept based on the predictab...

L. D. Post

1982-01-01

384

Rare Isotope Accelerators  

NASA Astrophysics Data System (ADS)

The next frontier for low-energy nuclear physics involves experimentation with accelerated beams of short-lived radioactive isotopes. A new facility, the Rare Isotope Accelerator (RIA), is proposed to produce large amount of these rare isotopes and post-accelerate them to energies relevant for studies in nuclear physics, astrophysics and the study of fundamental interactions at low energy. The basic science motivation for this facility will be introduced. The general facility layout, from the 400 kW heavy-ion superconducting linac used for production of the required isotopes to the novel production and extraction schemes and the highly efficient post-accelerator, will be presented. Special emphasis will be put on a number of technical breakthroughs and recent R&D results that enable this new facility.

Savard, Guy

2002-04-01

385

Introduction to Acceleration Mechanisms.  

National Technical Information Service (NTIS)

This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, ...

R. B. Palmer

1987-01-01

386

Accelerated Corrosion Testing.  

National Technical Information Service (NTIS)

Available methods for accelerated testing of corrosion behavior yield results which are not sufficiently accurate or reliable for predicting the service life of aircraft components and materials which degrade or fail due to environmental attack. Research ...

M. Khobaib

1982-01-01

387

Accelerating Translational Research  

Cancer.gov

Accelerating Translational Research Coordinating and facilitating translational research initiatives across the NCI and the cancer research community. NCI Translational Science Meetings NCI Translates - July 28-29, 2011 NCI Translates - 2009 NCI Translates

388

Wake field acceleration experiments  

SciTech Connect

Where and how will wake field acceleration devices find use for other than, possibly, accelerators for high energy physics. I don't know that this can be responsibly answered at this time. What I can do is describe some recent results from an ongoing experimental program at Argonne which support the idea that wake field techniques and devices are potentially important for future accelerators. Perhaps this will spawn expanded interest and even new ideas for the use of this new technology. The Argonne program, and in particular the Advanced Accelerator Test Facility (AATF), has been reported in several fairly recent papers and reports. But because this is a substantially new audience for the subject, I will include a brief review of the program and the facility before describing experiments. 10 refs., 7 figs.

Simpson, J.D.

1988-01-01

389

Inductive Plasma Accelerator Development.  

National Technical Information Service (NTIS)

The work described in the report comprises: (a) Theoretical studies of the performance of an electromagnetic induction plasma accelerator for radiation-cooled applications, and for pulsed operation. (b) The improvement of pre-existing instrumentation for ...

G. Fonda-Bonardi R. Rosen

1968-01-01

390

Broadband Accelerator Control Network.  

National Technical Information Service (NTIS)

A broadband data communications network has been implemented at BNL for control of the Alternating Gradient Synchrotron (AG) proton accelerator, using commercial CATV hardware, dual coaxial cables as the communications medium, and spanning 2.0 km. A 4 MHz...

J. Skelly T. Clifford R. Frankel

1983-01-01

391

Challenges in Linear Accelerator Radiotherapy for Chordomas and Chondrosarcomas of the Skull Base: Focus on Complications  

SciTech Connect

Purpose: Intracranial chordomas and chondrosarcomas are histologically low-grade, locally invasive tumors that infiltrate the skull base. Currently, consensus therapy includes surgical resection and adjuvant radiotherapy. Radiation delivery is typically limited by the proximity of these tumors to critical skull base structures. Methods: This is a retrospective review of 13 cases of chordomas and 2 cases of chondroid chondrosarcomas of the skull based treated with linear accelerator stereotactic radiotherapy (SRT, n = 10) or stereotactic radiosurgery (SRS, n = 5). The average time to the most recent follow-up visit was 4.5 years. The tumor characteristics, treatment details, and outcomes were recorded. Each radiation plan was reviewed, and the dosage received by the brainstem, optic apparatus, and pituitary was calculated. Results: Of the 10 patients treated with SRT, 6 were found to have unchanged or decreased tumor size as determined from radiographic follow-up. Of the 5 patients treated with SRS, 3 were found to have stable or unchanged tumors at follow-up. The complications included 1 SRT patient who developed endocrinopathy, 2 patients (1 treated with SRS and the other with SRT), who developed cranial neuropathy, and 1 SRS patient who developed visual deficits. Additionally, 1 patient who received both SRS and SRT within 2 years for recurrence experienced transient medial temporal lobe radiation changes that resolved. Conclusions: Where proton beam therapy is unavailable, linear accelerator-based SRT or radiosurgery remains a safe option for adjuvant therapy of chordomas and chondrosarcomas of the skull base. The exposure of the optic apparatus, pituitary stalk, and brainstem must be considered during planning to minimize complications. If the optic apparatus is included in the 80% isodose line, it might be best to fractionate therapy. Exposure of the pituitary stalk should be kept to <30 Gy to minimize endocrine dysfunction. Brainstem exposure should be limited to <60 Gy in fractions.

Hauptman, Jason S., E-mail: jhauptman@mednet.ucla.edu [Division of Stereotactic and Functional Neurosurgery, Department of Neurosurgery, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA (United States); Barkhoudarian, Garni; Safaee, Michael; Gorgulho, Alessandra [Division of Stereotactic and Functional Neurosurgery, Department of Neurosurgery, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA (United States); Tenn, Steven; Agazaryan, Nzhde; Selch, Michael [Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA (United States); De Salles, Antonio A.F. [Division of Stereotactic and Functional Neurosurgery, Department of Neurosurgery, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA (United States); Department of Radiation Oncology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA (United States)

2012-06-01

392

Collective field accelerator  

DOEpatents

A collective field accelerator which operates with a vacuum diode and utilizes a grooved cathode and a dielectric anode that operates with a relativistic electron beam with a .nu./.gamma. of .about. 1, and a plurality of dielectric lenses having an axial magnetic field thereabout to focus the collectively accelerated electrons and ions which are ejected from the anode. The anode and lenses operate as unoptimized r-f cavities which modulate and focus the beam.

Luce, John S. (Livermore, CA)

1978-01-01

393

Motion with Constant Acceleration  

NSDL National Science Digital Library

The purpose of this experiment is to track the motion for an air cart on a sloped track to fall a distance x with constant acceleration a = g sinq. You will verify that the distance and velocity along the incline are given by the parabola x = xo + vo t +1/2at2 and the line v = vo +at. Finally, you will determine the acceleration due to gravity.

Herman, Russell

2008-02-19

394

CEBAF Accelerator Achievements  

NASA Astrophysics Data System (ADS)

In the past decade, nuclear physics users of Jefferson Lab's Continuous Electron Beam Accelerator Facility (CEBAF) have benefited from accelerator physics advances and machine improvements. As of early 2011, CEBAF operates routinely at 6 GeV, with a 12 GeV upgrade underway. This article reports highlights of CEBAF's scientific and technological evolution in the areas of cryomodule refurbishment, RF control, polarized source development, beam transport for parity experiments, magnets and hysteresis handling, beam breakup, and helium refrigerator operational optimization.

Chao, Y. C.; Drury, M.; Hovater, C.; Hutton, A.; Krafft, G. A.; Poelker, M.; Reece, C.; Tiefenback, M.

2011-05-01

395

APT accelerator. Topical report  

Microsoft Academic Search

The Accelerator Production of Tritium (APT) project, sponsored by Department of Energy Defense Programs (DOE\\/DP), involves the preconceptual design of an accelerator system to produce tritium for the nation`s stockpile of nuclear weapons. Tritium is an isotope of hydrogen used in nuclear weapons, and must be replenished because of radioactive decay (its half-life is approximately 12 years). Because the annual

G. Lawrence; D. Rusthoi

1995-01-01

396

Self-motion perception during conflicting visual-vestibular acceleration.  

PubMed

Self-motion is known to be falsely perceived during exposure to the movement of visual surroundings. This illusory perception of visually-induced self-motion is known as "vection." The present study was conducted to examine the relative strengths of vection versus whole-body angular acceleration as they determine perceived self-rotation under conditions in which they individually provide conflicting information. Each subject was rotated for 90 s about a vertical axis at a constant acceleration, and a large-field visual surround in front of the subject was simultaneously rotated at a constant acceleration in the same direction, but at a magnitude of acceleration twice that of the body. This stimulus condition creates a sensory conflict between information from the vestibular/somatosensory systems and information from the visual system with respect to the direction of self-rotation. The subject eventually perceived self-acceleration in the direction of circular vection (CV), even though he or she was actually being accelerated in the direction opposite to CV. When the magnitude of contradictory chair acceleration exceeded the vestibular perceptual threshold, the onset latency of CV was significantly delayed. Our results suggest that visual information contributes to the perception of self-acceleration, and that illusory self-motion could overwhelm the feeling of self-acceleration due to inertial motion. CV would thus be a significant factor in determining spatial orientation in certain operational environments and flight conditions. PMID:19542600

Ishida, Masayuki; Fushiki, Hiroaki; Nishida, Hiroshi; Watanabe, Yukio

2008-01-01

397

Exposure from residual radiation after synchrotron shutdown  

Microsoft Academic Search

Personnel exposure from residual radiation present after an accelerator is shutdown for preventative or corrective maintenance is an important aspect that governs the manner in which a light ion facility can be used. This radiation is not only a safety issue for maintenance personnel but also can affect the patient throughput of the facility. Measurements were made with survey instruments

M. F. Moyers; D. A. Lesyna

2009-01-01

398

Effect of simultaneous exposure to toluene and xylene on their respective biological exposure indices in humans  

Microsoft Academic Search

Summary Studies that specifically address the influence of controlled human exposure to a combination of solvents on the biological monitoring of exposure are limited in number. The present study was undertaken to investigate whether simultaneous exposure of human volunteers to toluene and xylene could modify the respective metabolic disposition of these solvents. Five adult Caucasian men were exposed for 7

R. Tardif; S. Laparé; G. L. Plaa; J. Brodeur

1991-01-01

399

Laser Plasma Accelerators  

NASA Astrophysics Data System (ADS)

The continuing development of powerful laser systems has permitted to extend the interaction of laser beams with matter far into the relativistic domain, and to demonstrate new approaches for producing energetic particle beams. The extremely large electric fields, with amplitudes exceeding the TV/m level, that are produced in plasma medium are of relevance particle acceleration. Since the value of this longitudinal electric field, 10,000 times larger than those produced in conventional radio-frequency cavities, plasma accelerators appear to be very promising for the development of compact accelerators. The incredible progresses in the understanding of laser plasma interaction physic, allows an excellent control of electron injection and acceleration. Thanks to these recent achievements, laser plasma accelerators deliver today high quality beams of energetic radiation and particles. These beams have a number of interesting properties such as shortness, brightness and spatial quality, and could lend themselves to applications in many fields, including medicine, radio-biology, chemistry, physics and material science,security (material inspection), and of course in accelerator science.

Malka, Victor

400

Accelerated Reader: What Are the Lasting Effects on the Reading Habits of Middle School Students Exposed to Accelerated Reader in Elementary Grades?  

ERIC Educational Resources Information Center

|Investigates whether seventh-grade students who were exposed to the Accelerated Reader during elementary school tend to do more reading of books than those who did not have such exposure. Describes Accelerated Reader, a program in which books are given a point value on the basis of length and reading level. Proposes that students do not become…

Pavonetti, Linda M.; Brimmer, Kathyrn M.; Cipielewski, James F.

2003-01-01

401

Accelerated cleanup risk reduction  

SciTech Connect

There is no proven technology for remediating contaminant plume source regions in a heterogeneous subsurface. This project is an interdisciplinary effort to develop the requisite new technologies so that will be rapidly accepted by the remediation community. Our technology focus is hydrous pyrolysis/oxidation (HPO) which is a novel in situ thermal technique. We have expanded this core technology to leverage the action of steam injection and place an in situ microbial filter downstream to intercept and destroy the accelerated movement of contaminated groundwater. Most contaminant plume source regions, including the chlorinated solvent plume at LLNL, are in subsurface media characterized by a wide range in hydraulic conductivity. At LLNL, the main conduits for contaminant transport are buried stream channels composed of gravels and sands; these have a hydraulic conductivity in the range of 10{sup -1} to 10{sup -2} cm/s. Clay and silt units with a hydraulic conductivity of 10{sup -1} to 10{sup -6} cm/s bound these buried channels; these are barriers to groundwater movement and contain the highest contaminant concentrations in the source region. New remediation technologies are required because the current ones preferentially access the high conductivity units. HPO is an innovative process for the in situ destruction of contaminants in the entire subsurface. It operates by the injection of steam. We have demonstrated in laboratory experiments that many contaminants rapidly oxidize to harmless compounds at temperatures easily achieved by injecting steam, provided sufficient dissolved oxygen is present. One important challenge in a heterogeneous source region is getting heat, contaminants, and an oxidizing agent in the same place at the same time. We have used the NUFT computer program to simulate the cyclic injection of steam into a contaminated aquifer for design of a field demonstration. We used an 8 hour, steam/oxygen injection cycle followed by a 56 hour relaxation period in which the well was `capped`. Our results show the formation of an inclined gas phase during injection and a fast collapse of the steam zone within an hour of terminating steam injection. The majority of destruction occurs during the collapse phase, when contaminant laden water is drawn back towards the well. Little to no noncondensible gasses are created in this process, removing any possibility of sparging processes interfering with contaminant destruction. Our models suggest that the thermal region should be as hot and as large as possible. To have HPO accepted, we need to demonstrate the in situ destruction of contaminants. This requires the ability to inexpensively sample at depth and under high temperatures. We proved the ability to implies monitoring points at depths exceeding 150 feet in highly heterogeneous soils by use of cone penetrometry. In addition, an extractive system has been developed for sampling fluids and measuring their chemistry under the range of extreme conditions expected. We conducted a collaborative field test of HPO at a Superfund site in southern California where the contaminant is mainly creosote and pentachlorophenol. Field results confirm the destruction of contaminants by HPO, validate our field design from simulations, demonstrate that accurate field measurements of the critical fluid parameters can be obtained using existing monitoring wells (and minimal capital cost) and yield reliable cost estimates for future commercial application. We also tested the in situ microbial filter technology as a means to intercept and destroy the accelerated flow of contaminants caused by the injection of steam. A series of laboratory and field tests revealed that the selected bacterial species effectively degrades trichloroethene in LLNL Groundwater and under LLNL site conditions. In addition, it was demonstrated that the bacteria effectively attach to the LLNL subsurface media. An in-well treatability study indicated that the bacteria initially degrade greater than 99% of the contaminant, to concentrations less than regulatory limit

Knapp, R.B.; Aines, R.M.; Blake, R.G.; Copeland, A.B.; Newmark, R.L.; Tompson, A.F.B.

1998-02-01

402

Proton acceleration by circularly polarized traveling electromagnetic wave  

NASA Astrophysics Data System (ADS)

The acceleration of charged particles, producing collimated monoenergetic beams, over short distances holds the promise to offer new tools in medicine and diagnostics. Here, we consider a possible mechanism for accelerating protons to high energies by using a phase modulated circularly polarized electromagnetic wave propagating along a constant magnetic field. It is observed that a plane wave with dimensionless amplitude of 0.1 is capable to accelerate a 1 keV proton to 386 MeV under optimum conditions. Finally, we discuss possible limitations of the acceleration scheme.

Holkundkar, Amol; Brodin, Gert; Marklund, Mattias

2012-09-01

403

HRIBF Tandem Accelerator Radiation Safety System Upgrade  

SciTech Connect

The HRIBF Tandem Accelerator Radiation Safety System was designed to permit experimenters and operations staff controlled access to beam transport and experiment areas with accelerated beam present. Neutron-Gamma detectors are mounted in eaeh area at points of maximum dose rate and the resulting signals are integrated by redundan~ circuitry; beam is stopped if dose rate or integrated dose exceeds established limits. This paper will describe the system, in use for several vears at the HRIBF, and discuss changes recently made to modernize the system and to make the system compliant with DOE Order 5480.25 and related ORNL updated safety rules.

Blankenship, J.L.; Juras, R.C.

1998-11-04

404

Two-dimensional beat wave acceleration simulation  

SciTech Connect

Finite laser beam particle simulations of beat wave acceleration show that a coherent plasma wave excited by two-colinear laser beams at a difference frequency equal to the plasma frequency can produce maximum electron energies as predicted by simple one-dimensional theory. The time to saturation and the saturation amplitude of the plasma wave electric field agrees with the Rosenbluth-Liu theory. Stimulated Raman scattering does not appear to degrade the electron acceleration process. Eventually self-focussing and filamentation limit the lifetime of the coherent plasma wave to tens of picoseconds for an intense CO/sub 2/ laser beam.

Kindel, J.M.; Forslund, D.W.; Mori, W.B.; Joshi, C.; Dawson, J.M.

1984-01-01

405

Results from non-accelerator experiments  

SciTech Connect

The diversity of non-accelerator experiments is at first look both dazzling and even daunting. However, nearly all of these experiments strive to attain the same goal, to search for new physics, beyond the current Standard Model. These measurements are also unified in the fact that their results are often dominated by systematic uncertainties. This review necessarily covers only a limited subset of non-accelerator experiments, and will concentrate on the experimental areas where there has been significant recent progress. The topics reviewed include neutrino mazes, double beta decay, solar neutrino, and long-baseline neutrino oscillation measurements.

Wilkerson, J.F.

1992-01-01

406

Results from non-accelerator experiments  

SciTech Connect

The diversity of non-accelerator experiments is at first look both dazzling and even daunting. However, nearly all of these experiments strive to attain the same goal, to search for new physics, beyond the current Standard Model. These measurements are also unified in the fact that their results are often dominated by systematic uncertainties. This review necessarily covers only a limited subset of non-accelerator experiments, and will concentrate on the experimental areas where there has been significant recent progress. The topics reviewed include neutrino mazes, double beta decay, solar neutrino, and long-baseline neutrino oscillation measurements.

Wilkerson, J.F.

1992-12-31

407

TRACKING OF ACCELERATION WITH HNJ METHOD.  

SciTech Connect

After reviewing the principle of operation of acceleration with the method of Harmonic Number Jump (HNJ) in a Fixed-Field Alternating-Gradient (FFAG) accelerator for protons and heavy ions, we report in this talk the results of computer simulations performed to assess the capability and the limits of the method in a variety of practical situations. Though the study is not yet completed, and there still remain other cases to be investigated, nonetheless the tracking results so far obtained are very encouraging, and confirm the validity of the method.

RUGGIERO,A.G.

2007-11-05

408

Tracking of Acceleration with HNJ Method  

SciTech Connect

After reviewing the principle of operation of acceleration with the method of Harmonic Number Jump (HNJ) in a Fixed-Field Alternating Gradient (FFAG) accelerator for protons and heavy ions, we report in this talk the results of computer simulations performed to assess the capability and the limits of the method in a variety of practical situations. Though the study is not yet completed, and there still remain other cases to be investigated, nonetheless the tracking results so far obtained are very encouraging, and confirm the validity of the method.

Ruggiero,A.

2008-02-01

409

The APT Accelerator.*  

NASA Astrophysics Data System (ADS)

The accelerator for the Accelerator Production of Tritium (APT) project is a high-power RF linac designed to produce a 100-mA CW proton beam at an energy of 1300 MeV. A heavy-metal target produces large quantities of spallation neutrons, which are slowed to thermal energies and captured in a feed material to make tritium. The baseline accelerator design consists of a 75-keV proton injector, a 7-MeV radio-frequency quadrupole (RFQ), a 100-MeV coupled-cavity drift-tube linac (CCDTL), and a 1300-MeV side-coupled linac (SCL). The RFQ operates at a frequency of 350 MHz, while the CCDTL and SCL operate at 700-MHz. A quadrupole-magnet transport system conveys the 1300-MeV beam to production target/blanket assemblies where beam expanders using non-linear magnetic elements transform the linac output distribution into large-area rectangular distributions having a nearly uniform density. All the linac accelerating structures use conventional water-cooled copper technology. The SCL section is based on the well-proven 800-MeV LANSCE high-duty-factor linac at Los Alamos. The CCDTL is a new hybrid accelerating structure that combines the best features of the conventional drift-tube linac and the coupled-cavity linac to provide efficient and stable acceleration in the intermediate velocity range. Approximately 263 1-MW CW klystrons are needed to drive the 130-MW proton beam. The total ac-power requirement for the APT plant is about 438 MW, most of which is needed for the accelerator. An advanced-technology option is being considered that would replace the conventional SCL with a superconducting RF linac composed of sequences of 4-cell elliptical-type cavities. This option would reduce the electric power consumption significantly and would provide increased operational flexibility. * Work supported by the US Department of Energy.

Lawrence, George P.

1996-05-01

410

Mechanisms of Military Coatings Degradation: Accelerated and Outdoor Exposure Evaluations.  

National Technical Information Service (NTIS)

The Weapons and Materials Directorate of the U.S. Army Research Laboratory (ARL) has completed a 4-year research investigation on identifying and quantifying key degradation mechanisms of legacy and newly developed coatings systems used by the U.S. Army, ...

J. A. Escarsega W. S. Lum P. H. Patterson

2003-01-01

411

Physics of Laser-driven plasma-based acceleration  

SciTech Connect

The physics of plasma-based accelerators driven by short-pulse lasers is reviewed. This includes the laser wake-field accelerator, the plasma beat wave accelerator, the self-modulated laser wake-field accelerator, and plasma waves driven by multiple laser pulses. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse direction, electron dephasing, laser pulse energy depletion, as well as beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and plasmas with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Recent experimental results are summarized.

Esarey, Eric; Schroeder, Carl B.

2003-06-30

412

Energy Stabilization of Electrostatic Accelerators  

Microsoft Academic Search

Electrostatic accelerators, such as the Van de Graaf generator, are among the most established and well-developed particle accelerators. One of the key issues in the maturation of these accelerators has been the development of methods used to stabilize the energies of the particles they produce. Energy Stabilization of Electrostatic Accelerators presents a comprehensive overview of the key methods of stabilizing

J. Takács

1997-01-01

413

Plasma-based accelerator structures  

SciTech Connect

Plasma-based accelerators have the ability to sustain extremely large accelerating gradients, with possible high-energy physics applications. This dissertation further develops the theory of plasma-based accelerators by addressing three topics: the performance of a hollow plasma channel as an accelerating structure, the generation of ultrashort electron bunches, and the propagation of laser pulses is underdense plasmas.

Schroeder, Carl B.

1999-12-01

414

Example Exposure Scenarios.  

National Technical Information Service (NTIS)

Exposure scenarios are a tool to help the assessor develop estimates of exposure, dose, and risk. An exposure scenario generally includes facts, data, assumptions, inferences, and sometimes professional judgment about how the exposure takes place. The hum...

2004-01-01

415

Deuterium accelerator experiments for APT.  

SciTech Connect

Sandia National Laboratories in California initiated an experimental program to determine whether tritium retention in the tube walls and permeation through the tubes into the surrounding coolant water would be a problem for the Accelerator Production of Tritium (APT), and to find ways to mitigate the problem, if it existed. Significant holdup in the tube walls would limit the ability of APT to meet its production goals, and high levels of permeation would require a costly cleanup system for the cooling water. To simulate tritium implantation, a 200 keV accelerator was used to implant deuterium into Al 6061-T and SS3 16L samples at temperatures and particle fluxes appropriate for APT, for times varying between one week and five months. The implanted samples were characterized to determine the deuterium retention and Permeation. During the implantation, the D(d,p)T nuclear reaction was used to monitor the build-up of deuterium in the implant region of the samples. These experiments increased in sophistication, from mono-energetic deuteron implants to multi-energetic deuteron and proton implants, to more accurately reproduce the conditions expected in APT. Micron-thick copper, nickel, and anodized aluminum coatings were applied to the front surface of the samples (inside of the APT walls) in an attempt to lower retention and permeation. The reduction in both retention and permeation produced by the nickel coatings, and the ability to apply them to the inside of the APT tubes, indicate that both nickel-coated Al 6061-T6 and nickel-coated SS3 16L tubes would be effective for use in APT. The results of this work were submitted to the Accelerator Production of Tritium project in document number TPO-E29-Z-TNS-X-00050, APT-MP-01-17.

Causey, Rion A. (Sandia National Laboratories, Livermore, CA); Hertz, Kristin L. (Sandia National Laboratories, Livermore, CA); Cowgill, Donald F. (Sandia National Laboratories, Livermore, CA)

2005-08-01

416

Linear induction accelerators  

SciTech Connect

The development of linear induction accelerators has been motivated by applications requiring high-pulsed currents of charged particles at voltages exceeding the capability of single-stage, diode-type accelerators and at currents too high for rf accelerators. In principle, one can accelerate charged particles to arbitrarily high voltages using a multi-stage induction machine, but the 50-MeV, 10-kA Advanced Test Accelerator (ATA) at LLNL is the highest voltage machine in existence at this time. The advent of magnetic pulse power systems makes sustained operation at high-repetition rates practical, and this capability for high-average power is very likely to open up many new applications of induction machines in the future. This paper surveys the US induction linac technology with primary emphasis on electron machines. A simplified description of how induction machines couple energy to the electron beam is given, to illustrate many of the general issues that bound the design space of induction linacs.

Briggs, R.J.

1986-06-01

417

Advanced accelerator theory development  

SciTech Connect

A new accelerator technology, the dielectric wall accelerator (DWA), is potentially an ultra compact accelerator/pulsed power driver. This new accelerator relies on three new components: the ultra-high gradient insulator, the asymmetric Blumlein and low jitter switches. In this report, we focused our attention on the first two components of the DWA system the insulators and the asymmetric Blumlein. First, we sought to develop the necessary design tools to model and scale the behavior of the high gradient insulator. To perform this task we concentrated on modeling the discharge processes (i.e., initiation and creation of the surface discharge). In addition, because these high gradient structures exhibit favorable microwave properties in certain accelerator configurations, we performed experiments and calculations to determine the relevant electromagnetic properties. Second, we performed circuit modeling to understand energy coupling to dynamic loads by the asymmetric Blumlein. Further, we have experimentally observed a non-linear coupling effect in certain asymmetric Blumlein configurations. That is, as these structures are stacked into a complete module, the output voltage does not sum linearly and a lower than expected output voltage results. Although we solved this effect experimentally, we performed calculations to understand this effect more fully to allow better optimization of this DWA pulse-forming line system.

Sampayan, S.E.; Houck, T.L.; Poole, B.; Tishchenko, N.; Vitello, P.A.; Wang, I.

1998-02-09

418

Influence of feedbacks in the RF accelerating system and feeders between RF power generators and accelerating resonators on the in-phase dipole oscillations of bunches in cyclic accelerators  

NASA Astrophysics Data System (ADS)

In cyclic accelerators, interaction of the beam with the RF accelerating system may generate inphase dipole oscillations of bunches, which govern the limiting current of charged particles in the accelerator. A method of calculating the influence of the parameters of the RF system on the limit current is suggested. It is shown that feedbacks stabilizing the performance of the RF system considerably influence the limiting current in the accelerator. Moreover, the length of feeders through which the power of RF generators is applied to accelerating resonators also has an effect on the limiting current. The efficiency of the method is demonstrated by calculating the limiting electron current in a Sibir'-2 storage ring installed at the Russian Research Centre Kurchatov Institute.

Mityanina, N. V.; Petrov, V. M.

2011-10-01

419

Microelectromechanical acceleration-sensing apparatus  

SciTech Connect

An acceleration-sensing apparatus is disclosed which includes a moveable shuttle (i.e. a suspended mass) and a latch for capturing and holding the shuttle when an acceleration event is sensed above a predetermined threshold level. The acceleration-sensing apparatus provides a switch closure upon sensing the acceleration event and remains latched in place thereafter. Examples of the acceleration-sensing apparatus are provided which are responsive to an acceleration component in a single direction (i.e. a single-sided device) or to two oppositely-directed acceleration components (i.e. a dual-sided device). A two-stage acceleration-sensing apparatus is also disclosed which can sense two acceleration events separated in time. The acceleration-sensing apparatus of the present invention has applications, for example, in an automotive airbag deployment system.

Lee, Robb M. (Albuquerque, NM); Shul, Randy J. (Albuquerque, NM); Polosky, Marc A. (Albuquerque, NM); Hoke, Darren A. (Albuquerque, NM); Vernon, George E. (Rio Rancho, NM)

2006-12-12

420

75 FR 25279 - Device Improvements to Reduce the Number of Under-Doses, Over-Doses, and Misaligned Exposures...  

Federal Register 2010, 2011, 2012, 2013

...Misaligned Exposures From Therapeutic Radiation; Public Meeting; Request for Comments...Misaligned Exposures from Therapeutic Radiation.'' The purpose of this meeting is...manufacturers of linear accelerators, radiation therapy treatment planning...

2010-05-07

421

Accelerated degradation testing of a photovoltaic module  

NASA Astrophysics Data System (ADS)

There are a great many photovoltaic (PV) modules installed around the world. Despite this, not enough is known about the reliability of these modules. Their electrical power output decreases with time mainly as a result of the effects of corrosion, encapsulation discoloration, and solder bond failure. The failure of a PV module is defined as the point where the electrical power degradation reaches a given threshold value. Accelerated life tests (ALTs) are commonly used to assess the reliability of a PV module. However, ALTs provide limited data on the failure of a module and these tests are expensive to carry out. One possible solution is to conduct accelerated degradation tests. The Wiener process in conjunction with the accelerated failure time model makes it possible to carry out numerous simulations and thus to determine the failure time distribution based on the aforementioned threshold value. By this means, the failure time distribution and the lifetime (mean and uncertainty) can be evaluated.

Charki, Abdérafi; Laronde, Rémi; Bigaud, David

2013-01-01

422

Primary prevention: exposure reduction, skin exposure and respiratory protection.  

PubMed

Interventions for the primary prevention of occupational asthma have been reported in the medical literature, understanding the effectiveness of these efforts could help future interventions. The aim of our study was to evaluate the existing knowledge regarding the impact of controlling work exposure on the prevention of occupational asthma. We conducted systematic literature searches through April 2010 to examine if control of workplace exposures is effective for primary prevention of sensitisation and occupational asthma. The literature search for primary prevention of occupational asthma yielded 29 studies. Assessment of the available information led to the following conclusions and recommendations concerning primary prevention of occupational asthma. Exposure elimination is the strongest and preferred primary preventive approach to reduce the burden of occupational asthma. If elimination is not possible, exposure reduction is the second best option for primary prevention of occupational asthma. The evidence for the effectiveness of respirators in preventing occupational asthma is limited, and other options higher in the list of controls for occupational exposures, notably eliminating or minimising exposures at the source or in the environment, should be used preferentially. There is strong evidence to recommend not using powdered allergen-rich natural rubber latex gloves. There is weak evidence that suggests workers should minimise skin exposure to asthma-inducing agents. PMID:22654083

Heederik, Dick; Henneberger, Paul K; Redlich, Carrie A

2012-06-01

423

Accelerator Technology Program  

NASA Astrophysics Data System (ADS)

Highlights of major projects in the Accelerator Technology Division of the Los Alamos National Laboratory are presented. The first section deals with the Fusion Materials Irradiation Test Facility's 2-MeV accelerator on which tests began in May, as scheduled. Then, activities are reported on beam dynamics, inertial fusion, structure development, the racetrack microtron, the CERN high-energy physics experiment NA-12, and LAMPF II. The Proton Storage Ring is discussed next, with emphasis on the computer control system, diagnostics interfacing, and theoretical support. Other sections summarize progress on a portable radiographic linac, developments on the klystron code, and on permanent magnets. Activities of the Theory and Simulation Group are outlined next, followed by discussion of the oscillator experiment and the energy-recovery experiment in the free electron laser project. The last section reports on the accelerator test stand.

Jameson, R. A.

1984-07-01

424

The impact of Einstein's theory of special relativity on particle accelerators  

Microsoft Academic Search

We describe the consequences of the theory of special relativity on particle accelerators and present a historical overview of their evolution and contributions to science and the present limitations of existing accelerator technology. We report recent results of our experiment where we succeeded in accelerating relativistic electrons with visible light in vacuum. The experimental demonstration is the first of its

Tomas Plettner; Robert L Byer; Robert H Siemann

2005-01-01

425

Biological effects from electromagnetic field exposure and public exposure standards.  

PubMed

During recent years there has been increasing public concern on potential health risks from power-frequency fields (extremely low frequency electromagnetic fields; ELF) and from radiofrequency/microwave radiation emissions (RF) from wireless communications. Non-thermal (low-intensity) biological effects have not been considered for regulation of microwave exposure, although numerous scientific reports indicate such effects. The BioInitiative Report is based on an international research and public policy initiative to give an overview of what is known of biological effects that occur at low-intensity electromagnetic fields (EMFs) exposure. Health endpoints reported to be associated with ELF and/or RF include childhood leukaemia, brain tumours, genotoxic effects, neurological effects and neurodegenerative diseases, immune system deregulation, allergic and inflammatory responses, breast cancer, miscarriage and some cardiovascular effects. The BioInitiative Report concluded that a reasonable suspicion of risk exists based on clear evidence of bioeffects at environmentally relevant levels, which, with prolonged exposures may reasonably be presumed to result in health impacts. Regarding ELF a new lower public safety limit for habitable space adjacent to all new or upgraded power lines and for all other new constructions should be applied. A new lower limit should also be used for existing habitable space for children and/or women who are pregnant. A precautionary limit should be adopted for outdoor, cumulative RF exposure and for cumulative indoor RF fields with considerably lower limits than existing guidelines, see the BioInitiative Report. The current guidelines for the US and European microwave exposure from mobile phones, for the brain are 1.6 W/Kg and 2 W/Kg, respectively. Since use of mobile phones is associated with an increased risk for brain tumour after 10 years, a new biologically based guideline is warranted. Other health impacts associated with exposure to electromagnetic fields not summarized here may be found in the BioInitiative Report at www.bioinitiative.org. PMID:18242044

Hardell, Lennart; Sage, Cindy

2007-12-31

426

Acceleration of metal plates  

SciTech Connect

High-explosive charges have been used to accelerate stainless steel plates to velocities of 6-7 km/s. A two-stage system has been used in which the first stage is a plane-wave detonating system that accelerates the plate down a short barrel. The second stage consists of a hollow cylindrical charge through which the moving plate passes. After an adjustable delay this charge is detonated on the outer circumference of the entry side of the charge. Flash radiographs and witness plates show no breakup in the first stage but bowing and frequent breakup in the second stage. 6 figs.

Marsh, S.P.; McQueen, R.G.; Tan, T.H.

1989-01-01

427

Interfacing to accelerator instrumentation  

SciTech Connect

As the sensory system for an accelerator, the beam instrumentation provides a tremendous amount of diagnostic information. Access to this information can vary from periodic spot checks by operators to high bandwidth data acquisition during studies. In this paper, example applications will illustrate the requirements on interfaces between the control system and the instrumentation hardware. A survey of the major accelerator facilities will identify the most popular interface standards. The impact of developments such as isochronous protocols and embedded digital signal processing will also be discussed.

Shea, T.J.

1995-12-31

428

Accelerator technology program  

NASA Astrophysics Data System (ADS)

Highlights in beam dynamics, accelerator inertial fusion, radio frequency structure development, the racetrack microtron, CERN high energy physics experiment NA-12, and high flux radiographic linac study are reported. Selected proton Storage Ring activities and an update on the free electron laser are discussed. The fusion materials irradiation test facility work and progress on the klystron development project and on the gyrocon project are examined. The activities of the newly formed theory and simulation group are outlined. Activities concerning the accelerator test stand for the neutral particle beam program are outlined.

Jameson, R. A.

1984-05-01

429

Photocathodes in accelerator applications  

SciTech Connect

Some electron accelerator applications require bursts of short pulses at high microscopic repetition rates and high peak brightness. A photocathode, illuminated by a mode-locked laser, is well suited to filling this need. The intrinsic brightness of a photoemitter beam is high; experiments are under way at Los Alamos to study the brightness of short bunches with high space charge after acceleration. A laser-illuminated Cs/sub 3/Sb photoemitter is located in the first rf cavity of an injector linac. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a streak camera.

Fraser, J.S.; Sheffield, R.L.; Gray, E.R.; Giles, P.M.; Springer, R.W.; Loebs, V.A.

1987-01-01

430

Particle acceleration in Blazars  

NASA Astrophysics Data System (ADS)

Understanding the variable emission of blazars observed with gamma-ray telescopes and Fermi has become a major challenge for theoretical models of particle acceleration. Here, we introduce a novel time-dependent emission model in which the maximum energy of particles is determined from a balance between Fermi type I and II acceleration energy gains and radiative energy losses, allowing for an explanation of both the characteristic spectral energy distribution of blazars and their intrinsic sub-hour variability. Additionally, we can determine the physical condition of the emitting plasma concerning its turbulence and typical shock speeds.

Weidinger, Matthias; Spanier, Felix

2011-06-01

431

Exposure Measurement Action Level and Occupational Environmental Variability.  

National Technical Information Service (NTIS)

The proposed Occupational Safety and Health Administration Health Standards define an exposure measurement action level as one half of the current permissible exposure limits. The action level is the point at which certain provisions of the proposed stand...

N. A. Leidel K. A. Busch W. E. Crouse

1975-01-01

432

Particle Acceleration at High-? Shock Waves  

NASA Astrophysics Data System (ADS)

First-order Fermi acceleration processes at ultrarelativistic (? ~ 5-30) shocks are studied with the method of Monte Carlo simulations. The accelerated particle spectra are obtained by integrating the exact particle trajectories in a turbulent magnetic field near the shock. The magnetic field model assumes finite-amplitude perturbations within a wide wavevector range and with a predefined wave power spectrum, which are imposed on the mean field component inclined at some angle to the shock normal. The downstream field structure is obtained as the compressed upstream field. We show that the main acceleration process at oblique shocks is the particle compression at the shock. Formation of energetic spectral tails is possible in a limited energy range for highly perturbed magnetic fields. Cut-offs in the spectra occur at low energies in the resonance range considered. We relate this feature to the structure of the magnetic field downstream of the shock, where field compression produces effectively 2D turbulence in which cross-field diffusion is very small. Because of the field compression downstream, the acceleration process is inefficient also in parallel high-? shocks for larger turbulence amplitudes, and features observed in oblique shocks are recovered. For small-amplitude perturbations, particle spectra are formed in a wide energy range and modifications of the acceleration process due to the existence of long-wave perturbations are observed. The critical turbulence amplitude for efficient acceleration at parallel shocks decreases with ?. We also study the influence of strong short-wave perturbations, generated downstream of the shock, on the particle acceleration processes at high-? shocks. The spectral indices obtained do not converge to the ``universal'' value ? ~ 4.2. Our results indicate inefficiency of the first-order Fermi process to generate high-energy cosmic rays at ultrarelativistic shocks with the perturbed magnetic field structures considered in the present work.

Niemiec, Jacek

2005-11-01

433

Testing accelerated weathering tests for appropriate weathering chemistry: Ozone filtered xenon arc  

Microsoft Academic Search

Ftir spectroscopy has been used to follow the weathering chemistry of a HALS and UVA free polyester\\/urethane and a HALS and UVA\\u000a free acrylic\\/melamine clearcoat cured on silicon wafers and subjected to exposure in Florida, Arizona, and in a number of\\u000a accelerated weathering tests. All accelerated tests except EMMAQUA-NTW, ozone filtered xenon arc, and 3M Proprietary exposures\\u000a distort the polyester\\/urethane’s

J. L. Gerlock; C. A. Peters; A. V. Kucherov; T. Misovski; C. M. Seubert; R. O. Carter; M. E. Nichols

2003-01-01

434

A REVIEW OF METHODS FOR DEVELOPING ACCELERATED TESTING CRITERIA  

Microsoft Academic Search

Accelerated vibration testing seeks to compress long service exposures to vibration into a reduced length laboratory test by increasing the amplitude and\\/or frequency of the applied inputs during the laboratory test relative to the amplitude and\\/or frequency experienced during service. This testing procedure provides an important tool that can reduce testing time associated with a new design and reduce time

Charles R. Farrar; Thomas A. Duffey; Phillip J. Cornwell; Matthew T. Bement

435

An Automatic Machine for Accelerated Weathering Tests on Concrete  

Microsoft Academic Search

The machine described has been designed for accelerated weathering of concrete surfaces. Its basis is a turntable on a vertical axis, carrying concrete exposure specimens which are subjected to the action of smoke, water sprays, cooling elements and heating elements. The machine accommodates 32 specimen slabs of concrete each measuring 2 ft. × 1 ft. × 2 in., and by

W R Crawford; L J Murdock

1943-01-01

436

Accelerated Corrosion Test for Aluminum-Zinc Alloy Coatings  

Microsoft Academic Search

An electrochemically monitored etching method has been developed to enable accelerated service life testing of aluminum\\/zinc alloy coatings with a dendritic microstructure. The method involved pre-exposure of materials to the etching solution to remove the most active phases from the coatings. This process simulated the early phases of atmospheric corrosion. The method significantly shortened the time required for an atmospheric

T. C. Simpson

1993-01-01

437

Radiative accelerations for evolutionary model calculations  

SciTech Connect

Monochromatic opacities from the OPAL database have been used to calculate radiative accelerations for the 21 included chemical species. The 10{sup 4} frequencies used are sufficient to calculate the radiative accelerations of many elements for T{gt}10{sup 5}K, using frequency sampling. This temperature limit is higher for less abundant elements. As the abundances of Fe, He, or O are varied, the radiative acceleration of other elements changes, since abundant elements modify the frequency dependence of the radiative flux and the Rosseland opacity. Accurate radiative accelerations for a given element can only be obtained by allowing the abundances of the species that contribute most to the Rosseland opacity to vary during the evolution and recalculating the radiative accelerations and the Rosseland opacity during the evolution. There are physical phenomena that cannot be included in the calculations if one uses only the OPAL data. For instance, one should correct for the momentum given to the electron in a photoionization. Such effects are evaluated using atomic data from Opacity Project, and correction factors are given. {copyright} {ital 1998} {ital The American Astronomical Society}

Richer, J.; Michaud, G. [Departement de Physique, Universite de Montreal, MontrealH3C3J7 (Canada); Rogers, F.; Iglesias, C. [Lawrence Livermore National Laboratory, PO Box 808, Livermore, California94550 (United States); Turcotte, S. [Departement de Physique, Universite de Montreal, MontrealH3C3J7 (Canada); LeBlanc, F. [Departement de Physique, Universite de Moncton, MonctonE1A3E9 (Canada)

1998-01-01

438

Environmental tobacco smoke exposure assessment  

SciTech Connect

Environmental tobacco smoke (ETS) is the material released into the environment as tobacco products are smoked. Cigarettes, pipes, and cigars all produce ETS but the term has become all but synonymous with indoor air contamination by cigarette smoking. This is because cigarettes are by far the most commonly consumed tobacco product and because the principal human exposure occurs indoors. Exposure to ETS is variously termed as passive smoking, involuntary smoking, and as exposure to second-hand smoke. Considerable progress has been made toward a better understanding of ETS exposure. Strengths and limitations of various measures of exposure are better understood and much data has been generated on the quantities of many ETS-constituents in many indoor environments. The properties of ETS, methods for its measurement in indoor air, and many results of field studies have recently been reviewed by the author. The recent EPA report includes a major treatment of exposure estimation including air concentrations, questionnaires, and biomarkers. This paper discusses approaches to exposure assessment and summarizes data on indoor air concentrations of ETS-constituents.

Guerin, M.R.

1993-01-01

439

Environmental tobacco smoke exposure assessment  

SciTech Connect

Environmental tobacco smoke (ETS) is the material released into the environment as tobacco products are smoked. Cigarettes, pipes, and cigars all produce ETS but the term has become all but synonymous with indoor air contamination by cigarette smoking. This is because cigarettes are by far the most commonly consumed tobacco product and because the principal human exposure occurs indoors. Exposure to ETS is variously termed as passive smoking, involuntary smoking, and as exposure to second-hand smoke. Considerable progress has been made toward a better understanding of ETS exposure. Strengths and limitations of various measures of exposure are better understood and much data has been generated on the quantities of many ETS-constituents in many indoor environments. The properties of ETS, methods for its measurement in indoor air, and many results of field studies have recently been reviewed by the author. The recent EPA report includes a major treatment of exposure estimation including air concentrations, questionnaires, and biomarkers. This paper discusses approaches to exposure assessment and summarizes data on indoor air concentrations of ETS-constituents.

Guerin, M.R.

1993-06-01

440

Particle accelerators test cosmological theory  

SciTech Connect

Over the past decade two subfields of science, cosmology and elementary-particle physics, have become married in a symbiotic relationship that has produced a number of exciting offspring. These offspring are beginning to yield insights on the creation of spacetime and matter at epochs as early as 10 to the minus 43 to 10 to the minus 35 second after the birth of the universe in the primordial explosion known as the big bang. Important clues to the nature of the big bang itself may even come from a theory currently under development, known as the ultimate theory of everything (T.E.O.). A T.E.O. would describe all the interactions among the fundamental particles in a single bold stroke. Now that cosmology ahs begun to make predictions about elementary-particle physics, it has become conceivable that those cosmological predictions could be checked with careful