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PubMed1999

Synchrotron radiation of crystallized beams.

We study the modifications of synchrotron radiation of charges in a storage ring as they are cooled. The pair correlation lengths between the charges are manifest in the synchrotron radiation and coherence effects exist for wavelengths longer than the coherence lengths between the charges. Therefore, the synchrotron radiation can be used as a diagnostic tool to determine the state (gas, liquid, crystal) of the charged plasma in the storage ring. We show also that the total power of the synchrotron radiation is significantly reduced for crystallized beams, both coasting and bunched. This opens the possibility of accelerating particles to ultrarelativistic energies using small-sized cyclic accelerators.

Journal Article↗

PubMed1991

Plasma clearance of emulsified triolein in conscious rats: effects of phosphatidylcholine species, cholesterol content and emulsion surface physical state.

In vivo clearance of an emulsified triglyceride from rat plasma is strongly influenced by the phosphatidylcholine molecular species and the cholesterol content of the emulsion. Chylomicron-sized, glycerol-tri[9,10-3H]oleate (triolein)-sonicated emulsions containing 2-3 or 9-14 mol% unesterified cholesterol and specific phosphatidylcholines (egg, dimyristoyl, dipalmitoyl, distearoyl) were prepared above the phospholipid gel----liquid crystalline transition temperatures and injected intravenously into awake, non-fasting rats in bolus doses of 1-3 mg lipid. The emulsified triolein was cleared from plasma both by lipolysis during circulation and by uptake of emulsion particles or their remnants into tissues. Increasing the cholesterol content greatly accelerated particle clearance from plasma when emulsions were made with mixed-chain (egg) phosphatidylcholine, but prolonged their circulation time when the emulsions contained saturated phosphatidylcholines. The relative amounts cleared by reticuloendothelial versus liver parenchymal cells were influenced both by the cholesterol content and the phosphatidylcholine species of the emulsions. Significant triolein lipolysis in plasma occurred only with egg or dimyristoyl phosphatidylcholine emulsions containing 2-3% cholesterol and this lipolysis was blocked by increasing the cholesterol content. No lipolysis occurred when emulsions contained dipalmitoyl or distearoyl phosphatidylcholine, irrespective of cholesterol content.

Animals↗

PubMed1997

Assessment of dose equivalent due to neutrinos.

Neutrinos are present in the natural environment and are also produced by particle accelerators. A recent hypothesis has also been proposed that asserts that ionizing radiation due to neutrinos from certain astronomical events may have led to the extinction of some biological species. Thus, it is of interest to be able to estimate the dose equivalent due to these weakly interacting particles. Presented here are methods for estimating the dose equivalent due to neutrinos over a broad domain of energy, examples of such calculations, and an assessment of the postulated role of neutrinos in biological extinctions. It is concluded that the dose equivalent due to neutrinos from natural sources and from present-day accelerators is inconsequential and the postulated role of neutrinos in biological extinctions is highly improbable.

Calcium↗

PubMed2001

HZETRN: neutron and proton production in quasi-elastic scattering of GCR heavy-ions.

The development of transport models for radiation shielding design and evaluation has provided a series of deterministic computer codes that describe galactic cosmic radiation (GCR), solar particle events, and experimental beams at particle accelerators. These codes continue to be modified to accommodate new theory and improvements to the particle interaction database (Cucinotta et al., 1994, NASA Technical Paper 3472, US Government Printing Office, Washington DC). The solution employed by the heavy-ion transport code HZETRN was derived with the assumption that nuclear fragments are emitted with the same velocity as the incident ion through velocity conserving nuclear interactions. This paper presents a version of the HZETRN transport code that provides a more realistic distribution of the energy of protons and neutrons emitted from GCR interactions in shields. This study shows that the expected GCR dose equivalent is lower than previously calculated for water shields that are less than 110 g cm-2 thick. Calculations of neutron energy spectra in low Earth orbit indicate substantial contributions from relativistic neutrons.

Computer Simulation↗

PubMed2002

Electron acceleration by a wake field forced by an intense ultrashort laser pulse.

Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a high-intensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.

Journal Article↗

PubMed2004

Infrasound initiates directional fast-start escape responses in juvenile roach Rutilus rutilus.

Acoustic stimuli within the sonic range are effective triggers of C-type escape behaviours in fish. We have previously shown that fish have an acute sensitivity to infrasound also, with acceleration thresholds in the range of 10(-5) m s(-2). In addition, infrasound at high intensities around 10(-2) m s(-2) elicits strong and sustained avoidance responses in several fish species. In the present study, the possible triggering of C-escapes by infrasonic single-cycle vibrations was examined in juvenile roach Rutilus rutilus. The fish were accelerated in a controlled and quantifiable manner using a swing system. The applied stimuli simulated essential components of the accelerations that a small fish would encounter in the hydrodynamic flow field produced by a predatory fish. Typical C- and S-type escape responses were induced by accelerations within the infrasonic range with a threshold of 0.023 m s(-2) for an initial acceleration at 6.7 Hz. Response trajectories were on average in the same direction as the initial acceleration. Unexpectedly, startle behaviours mainly occurred in the trailing half of the test chamber, in which the fish were subjected to linear acceleration in combination with compression, i.e. the expected stimuli produced by an approaching predator. Very few responses were observed in the leading half of the test chamber, where the fish were subjected to acceleration and rarefaction, i.e. the stimuli expected from a suction type of predator. We conclude that particle acceleration is essential for the directionality of the startle response to infrasound, and that the response is triggered by the synergistic effects of acceleration and compression.

Acceleration↗

PubMed2005

Bunching instability of rotating relativistic electron layers and coherent synchrotron radiation.

We study the stability of a collision-less, relativistic, finite-strength, cylindrical layer of charged particles in free space by solving the linearized Vlasov-Maxwell equations and compute the power of the emitted electromagnetic waves. The layer is rotating in an external magnetic field parallel to the layer. This system is of interest to understanding the high brightness temperature of pulsars which cannot be explained by an incoherent radiation mechanism. Coherent synchrotron radiation has also been observed recently in bunch compressors used in particle accelerators. We consider equilibrium layers with a "thermal" energy spread and therefore a nonzero radial thickness. The particles interact with their retarded electromagnetic self-fields. The effect of the betatron oscillations is retained. A short azimuthal wavelength instability is found which causes a modulation of the charge and current densities. The growth rate is found to be an increasing function of the azimuthal wave number, a decreasing function of the Lorentz factor, and proportional to the square root of the total number of electrons. We argue that the growth of the unstable perturbation saturates when the trapping frequency of electrons in the wave becomes comparable to the growth rate. Owing to this saturation we can predict the radiation spectrum for a given set of parameters. Our predicted brightness temperatures are proportional to the square of the number of particles and scale by the inverse five-third power of the azimuthal wave number which is in rough accord with the observed spectra of radio pulsars.

Journal Article↗

PubMed1995

Genetic transformation of banana and plantain (Musa spp.) via particle bombardment.

We have developed a simple protocol to allow the production of transgenic banana plants. Foreign genes were delivered into embryogenic suspension cells using accelerated particles coated with DNA. Bombardment parameters were optimized for a modified particle gun resulting in high levels of transient expression of the beta-glucuronidase gene in both banana and plantain cells. Bombarded banana cells were selected with hygromycin and regenerated into plants. Molecular and histochemical characterization of transformants revealed the stable integration of the transferred genes into the banana genome.

Biolistics↗

PubMed2002

Plasma wakefield acceleration for ultrahigh-energy cosmic rays.

A cosmic acceleration mechanism is introduced which is based on the wakefields excited by the Alfvén shocks in a relativistically flowing plasma. We show that there exists a threshold condition for transparency below which the accelerating particle is collision-free and suffers little energy loss in the plasma medium. The stochastic encounters of the random accelerating-decelerating phases results in a power-law energy spectrum: f(epsilon) proportional, variant 1/epsilon(2). As an example, we discuss the possible production in the atmosphere of gamma ray bursts of ultrahigh-energy cosmic rays (UHECR) exceeding the Greisen-Zatsepin-Kuzmin cutoff. The estimated event rate in our model agrees with that from UHECR observations.

Journal Article↗

PubMed1980

On the mechanics of chromosomal aberrations: a study with single and multiple spatially-associated protons.

A unique radiation configuration, triads of protons, where mean separation between protons was controlled to be about 0.2 microns, has been used to irradiate Chinese hamster V79 cells. These triads of accelerated particles were more effective at producing chromosomal aberrations than randomly incident particles. Cells were irradiated with either single or three associated protons, with each proton depositing energy intracellularly at an LET of about 30 keV per micron. The associated protons were produced from accelerated molecular ions (H3+) that dissociated into atomic ions in a 6 mu Mylar foil on which the cells were growing, becoming triads of particles separated by a mean of about 0.2 microns in the cell nuclei. Chromosomal aberrations were scored from cells accumulated with colcemid over hourly intervals after irradiation. Those cells closest to mitosis (late G2) were the most sensitive to radiation, while overall "triple" protons were 52% more effective than single protons in producing aberrations. Only 10% of particles incident in nuclei resulted in an effect for the most sensitive period (late G2) dropping to 2% for the least sensitive period (early S--late G1). The frequencies of chromatid deletions declined dramatically with time post-irradiation, with isochromatid deletions less so and the frequencies of chromatid interchanges comparatively unchanged. Chromatid deletions and isochromatid deletions were often subtantially increased after "triple" proton irradiation, with the frequencies of chromatid interchanges less effected. This implies that both chromatid and isochromatid deletions can readily result from interactions between pairs of induced lesions about 0.2 microns apart. Achromatic lesions (gaps) were numerically equivalent after both irradiations implying a single lesion production mode. Results are compatible with there being a substantial short range component of interaction (less than 0.1 microns) between damaged sites, with a long range component of interaction extending to a few tenths of a micrometer.

Animals↗

PubMed2005

Channeling chaos by building barriers.

Chaotic diffusion often represents a severe obstacle for the setup of experiments, e.g., in fusion plasmas or particle accelerators. We present a complete test of a method of control of Hamiltonian chaos, with both its numerical test and its first experimental realization on a paradigm for wave-particle interaction, i.e., a travelling wave tube. The core of our approach is a small apt modification of the system which channels chaos by building barriers to diffusion. Its experimental realization opens the possibility to practically achieve the control of a wide range of systems at a low additional cost of energy.

Journal Article↗

PubMed2003

Accelerated immune response to DNA vaccines.

DNA vaccines offer considerable promise for improvement over conventional vaccines. For the crucial step of delivering DNA vaccines intracellularly, electroporation (EP) has proven to be highly effective. This method has yielded powerful humoral and cellular responses in various species, including nonhuman primates. In an attempt to further improve DNA vaccination we used micron-size gold particles (which do not bind or adsorb DNA) as a particulate adjuvant which was coinjected with DNA intramuscularly into mice, followed by EP of the target site. The presence of gold particles accelerated the antibody response significantly. Maximum titers against hepatitis B surface antigen (HBsAg) were reached after one boost in 6 weeks, whereas 8 weeks were required without particles. These immunizations were effective in protecting mice against tumor challenge with cancer cells expressing HBsAg as a surrogate cancer antigen. Computer modeling of electric fields and gene expression studies indicate that gold particles do not stimulate EP and subsequent antigen expression. The particles may act as an attractant for immune cells, especially antigen presenting cells. We conclude that particulate adjuvants combined with DNA vaccine delivery by EP reduces the immune response time and may increase vaccine efficacy. This method may become valuable for developing prophylactic as well as therapeutic vaccines. The rapid response may be of particular interest in countering bio-terrorism.

Adenocarcinoma↗

PubMed1996

The biological effectiveness of radon-progeny alpha particles. V. Comparison of oncogenic transformation by accelerator-produced monoenergetic alpha particles and by polyenergetic alpha particles from radon progeny.

Generation of estimates of risk caused by exposure to radon in the home, either from miner data or from A-bomb data, requires several scaling factors such as for dose, dose rate and radiation quality, and possible synergisms. Such scaling factors are best developed from laboratory-based studies. Two possible sources of alpha particles for such studies are (1) a polyenergetic spectrum, generated directly by radon and its progeny, or (2) a series of monoenergetic alpha particles. We compare here the results of oncogenic transformation from studies using both systems. At the Columbia University Radiological Research Accelerator Facility (RARAF), C3H 10T1/2 cells were irradiated with alpha particles of various energies, with defined LETs from 70 to 200 keV/mum. At Pacific Northwest Laboratory, cells from the same stock were exposed to alpha particles from radon gas and its progeny, which were in equilibrium with the culture medium. There was good agreement between the results of oncogenic transformation experiments using the two different exposure systems. Apart from the experimental transformation frequencies themselves, such a comparison requires (1) reliable dosimetry at both facilities and (2) estimated LET distributions for the polyenergetic alpha-particle irradiator. Thus this good agreement gives some confirmation to the technique which is used to fold together oncogenic transformation rates from monoenergetic alpha particles to yield a predicted rate for a spectrum of alpha particles.

Alpha Particles↗

PubMed2001

Simultaneous acceleration of multiply charged ions through a superconducting linac.

The possibility of simultaneously accelerating particles with a range of charge-to-mass ratios ( approximately 20%) to the same energy is proposed and demonstrated for a superconducting linac. Uranium ions stripped in a foil with eight charge states have been accelerated through a portion of the ATLAS linac from 286 to 690 MeV, with 94% of the injected uranium in the accelerated beam. Emittance of the resultant beam has been measured and the energy spread was 1.3% compared to 0.4% for a single charge state. This development has immediate application to the high-intensity acceleration of heavy ions that are limited by ion-source intensities, such as the proposed Rare Isotope Accelerator Facility.

Journal Article↗

PubMed2002

Persistence of a continuous stochastic process with discrete-time sampling: non-Markov processes.

We consider the problem of "discrete-time persistence," which deals with the zero crossings of a continuous stochastic process X(T) measured at discrete times T=nDeltaT. For a Gaussian stationary process the persistence (no crossing) probability decays as exp(-theta(D)T)=[rho(a)](n) for large n, where a=exp(-DeltaT/2) and the discrete persistence exponent theta(D) is given by theta(D)=(ln rho)/(2 ln a). Using the "independent interval approximation," we show how theta(D) varies with DeltaT for small DeltaT and conclude that experimental measurements of persistence for smooth processes, such as diffusion, are less sensitive to the effects of discrete sampling than measurements of a randomly accelerated particle or random walker. We extend the matrix method developed by us previously [Phys. Rev. E 64, 015101(R) (2001)] to determine rho(a) for a two-dimensional random walk and the one-dimensional random-acceleration problem. We also consider "alternating persistence," which corresponds to a<0, and calculate rho(a) for this case.

Journal Article↗

PubMed1972

Visual sensations induced by relativistic nitrogen nuclei.

The ability of the human eye to detect nitrogen nuclei that enter the retina at speeds just above the Cerenkov threshold has been confirmed in an experiment at the Princeton Particle Accelerator. A system for beam transport and subject alignment delivered individual nitrogen nuclei onto a spot 3 millimeters in diameter on the retina at a visual angle of 7 degrees on the temporal side of the fovea. The beam particles entered the retina within 25 degrees of normal and induced visual sensations that had the appearance of streaks for three out of four subjects.

Dark Adaptation↗

PubMed2001

Compressive properties of cancellous bone defects in a rabbit model treated with particles of natural bone mineral and synthetic hydroxyapatite.

A rabbit model was developed to evaluate the compressive mechanical properties of cancellous bone defects treated with particles of selected bone graft substitute materials. A novel feature of the model was the precise retrieval of the site of implantation. A notable finding was a 9-fold increase in the modulus of elasticity of the defect implanted with a synthetic hydroxyapatite material after 26 weeks when compared to the modulus of the trabecular bone normally at the site. The compressive modulus of lesions treated with particles of a natural bovine bone mineral (anorganic bovine bone) was closer to the normal modulus of the cancellous bone at the site. While the compressive strength of the anorganic bone particles was less than that of normal bone, the site implanted with the bone mineral particles achieved compressive strength greater than normal after 6 weeks. Moreover, the anorganic bone particles accelerated the increase in strength of the lesion, at 6 weeks exceeding the strength achieved by the untreated defect after 26 weeks. The potential problem associated with the disparity in the compressive modulus between sites implanted with the synthetic HA particles and surrounding bone is discussed.

Animals↗

PubMed2002

Alpha-tail production with ion-cyclotron-resonance heating of 4He-beam ions in JET plasmas.

Third-harmonic ion-cyclotron-resonance heating of 4He-beam ions has produced for the first time on the JET tokamak high-energy populations of 4He ions to simulate 3.5 MeV fusion-born alpha (alpha) particles. Acceleration of 4He ions to the MeV energy range is confirmed by gamma-ray emission from the nuclear reaction 9Be(alpha,ngamma) 12C and excitation of Alfvén eigenmodes. Concomitant electron heating and sawtooth stabilization are observed. The scheme could be used in next-step tokamaks to gain information on trapped alpha particles and to test alpha diagnostics in the early nonactivated phase of operation.

Journal Article↗