bluuebunny/crossref_metadata_2025_split huggingface dataset:
Short communicationKey differences between school lunches and packed lunches in primary schools in England in 2009
Authors: Pearce Jo , Harper Clare , Haroun Dalia , Wood Lesley , Nelson Michael 
Published: January 2011

AbstractObjectiveTo compare the key differences between school lunches and packed lunches as consumed in a nationally representative sample of primary schools, 6–8 months after the nutrient-based standards for school lunch became mandatory.DesignData on 6580 pupils’ school lunches and 3422 pupils’ packed lunches were collected between February and April 2009 from pupils attending primary schools in England. Fieldwork was conducted over five consecutive school days. Fieldworkers randomly selected ten pupils taking a school lunch and five pupils bringing a packed lunch each day at each school, and recorded and weighed all food and drink items consumed, as well as any leftovers.SettingA nationally representative sample of 136 state-maintained primary schools in England.SubjectsA total of 10 002 pupils aged 4–12 years.ResultsMean intakes of protein, fat, saturated fat and vitamin C from both types of lunch met the nutrient-based standards. Pupils taking school lunches on average consumed significantly more protein, NSP, vitamin A, folate and Zn and less fat, saturated fat, non-milk extrinsic sugars (NMES), Na, Ca, vitamin C and Fe than pupils taking packed lunches. Energy intakes were low in both groups.ConclusionsPacked lunches were less likely to accord with food-based or nutrient-based standards than school lunches. Higher levels of Na, NMES, fat and percentage energy from saturated fat emphasise the difficulties associated with optimising nutrient intakes from packed lunches.
Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules
Authors: Holm A. I. S. , Johansson H. A. B. , Cederquist H. , Zettergren H. 
Published: January 2011

We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H$^+$+-, C$_2$2H$_2$2-, and C$_2$2H$_2^+$2+-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion–PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAH$^{q+}$q+-molecules are thermodynamically stable for q ⩽ 2 (naphthalene, biphenylene, and anthracene), q ⩽ 3 (pyrene), and q ⩽ 4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H$^+$+-emissions from all five PAHs and for C$_2$2H$_2^{+}$2+-emission from naphthalene – the smallest PAH.
Theory of high-frequency heating of an inhomogeneous high-temperature plasma
Authors: Dolgopolov V.V. , Stepanov K.N. 
Published: January 2011

We investigate Čerenkov absorption by a plasma of the energy of an electromagnetic field created by azimuthal electric currents flowing in a long coil around a plasma cylinder. The density of external currents has the form of a traveling wave j=j0 cos (kz—ωt) δ (r—R) (R is the radius of the coil). The frequency of the field is considerably smaller than the ion cyclotron frequency. Gas-kinetic plasma pressure n0(Te + Ti) is assumed small compared with the magnetic pressure H0
2/8π. Plasma density n0, electron temperature Te and ion temperature Ti are taken to be functions of the radius.
In the present study expressions have been found for the energy absorbed by plasma per unit time. Absorption is maximal when the phase velocity of the wave ω/k is of the order of the thermal velocity of the ions νi = (Ti/mi)½ (mi is the ion mass). If the radius of the plasma is of the order of the radius of the coil and of the order of the wavelength 1/k, then for ω/k ∝ νi the mean energy gained by one particle per unit time, in order of magnitude, equals dW/df = H∼2ωTi/H0
2 where H∼ = 4πj0/c is the amplitude of the alternating magnetic field.
For a strongly non-isothermal plasma (Te ≫ Ti) heating increases drastically if the phase velocity of the wave is near the velocity of sound in a collisionless plasma νs = (Te/mi)½

Expressions have also been obtained for energy absorbed by an inhomogeneous plasma for coils of finite lengths.
Spatially periodic plasma structures appearing in fast heavy-current discharges
Authors: Kvartskhava I. F. , Kervalidze K. N. , Gvaladze Yu. S. , Zukakishvili G. G. 
Published: January 2011

We discuss recent theta- and z-pinch experiments performed to investigate the spatially periodic structure of a heavy-current plasma. A heavy-current plasma seeks to form a periodic structure whose basic elements are the E filaments (oriented along the electric field) and the H filaments (oriented perpendicular to the electric field). By means of Rogowski belts and magnetic probes we measured the distributions of plasma currents and magnetic fields. Almost all the plasma current was concentrated in the E filaments that are the elementary z pinches, whereas relatively very small currents flowed along the H filaments. The initial magnetic field stimulated plasma breakup into filaments that were parallel to the field lines. The E- and H-filament systems had a certain stability and they affected the discharge dynamics in a definite manner. Related to them in particular was the excitation of a “tongue” plasma instability in theta pinches.
We studied qualitatively several mechanisms that are possible in forming E- and H-filament systems and are based on plasma drift motion in sheared electric and magnetic fields.
Faust 1 — A hardcore discharge stability experiment
Authors: Aitken K.L. , Hopkins K.J. , Bickerton R.J. , Hardcastle R.A. , Reynolds P. 
Published: January 2011

A hardcore discharge stability experiment is described in which the final configuration is obtained by the radial inward collapse of the plasma sheath from the wall of the tube. By varying the initial conditions an axial field of arbitrary sign can be trapped within the annular plasma column. The construction and mode of operation of the apparatus is fully described.
The gas currents were the order of 50 kA and rod currents were 120 kA, so that the current in the gas was less than half that in the rod at all times. The general behaviour of the discharge was examined and the effects of pressure, preionization and trapped axial field studied. A detailed examination was made of a representative set of conditions with electric, magnetic and double Langmuir probes. These measurements, together with quantities derived from them, are discussed and the derived values of electron temperature and kinetic pressure are compared with the directly measured values. The validity of the pressure balance analysis is considered in the light of these results.
The discharge, without trapped axial field, showed a high degree of reproducibility and the observed fluctuations were of low amplitude (<10%) and low frequency (∼500kc/s) in both electric and magnetic field and in particle density. The last showed a well-defined annular sheath until late in the halfcycle; the radial profiles of azimuthal and axial current densities, kinetic pressure, temperature, and particle density showed good agreement. With trapped axial field, however, the discharge showed a reduction in stability, especially with trapped reverse field which introduces a null in the total axial field. Even with these, the most unstable conditions, the fluctuations were still relatively small (<20%) and of low frequency (∼1 Mc/s). The stability of the discharge is quantitatively compared with stability theory and the results discussed.
Hydromagnetic waves in a partially ionized hydrogen plasma
Authors: Malein A. 
Published: January 2011

This paper gives further experimental verification of the theory of fast hydromagnetic waves. By a suitable choice of plasma conditions the compressional wave is propagated in a partially ionized cylindrical hydrogen plasma at frequencies below the ion cyclotron frequency. The propagation constants of the wave are measured experimentally by observing the phase velocity and attenuation over a fixed distance. Other plasma parameters, with the exception of the neutral density are measured independently.
To obtain good experimental agreement with the theoretical curves computed from the measured data, it is necessary to postulate a considerable neutral particle density in the plasma. This gives rise to loading of the wave, observable as a reduction in the Alfvén speed, and also to wave damping not explicable by resistive effects alone. The enhanced loading produced by neutral particles is unaffected by variations in magnetic field and the fitted value of neutral density derived from wave cut-off data is in agreement with that calculated from attenuation measurements.
Self-consistent magnetic field and integrals of plasma motion
Authors: Lacina J. 
Published: January 2011

A general solution of the Vlasov equation for the stationary axisymmetric distribution function of charged particles in plasma, together with a self-consistent solution of the Maxwell equations.

is found and physically interpreted.
The orthogonal natural system of coordinates of a magnetic field jointly with magnetic induction B and the integrals of motion are first determined. The spatial dependence of the resultant magnetic field is discussed in considerable detail and criteria for the existence of minimum-B are established. It is indicated that currents in plasma itself create configurations with a minimum-B on the axis of symmetry under the following necessary and sufficient exact conditions. (1) There must exist a minimum value of B in the longitudinal direction at r = z = 0 (mirror field):

(2) It must be, at r = z = 0, that –(4π/c) (∂iφ/∂r)> ½∂2
B/∂z2, where r, φ, z are the cylindrical coordinates, and iφ the electric current in the plasma.
Factors determining beta in a theta-pinch experiment
Authors: Bodin H.A.B. , Dancy D.J. 
Published: January 2011

The containment and stability of the theta pinch depend critically upon the value of beta. However, while theoretical calculations predict a value of unity on the axis, experimental results show that the value on axis is substantially less than this.
The possibility that these low experimental values are due to a small field diffusion in the early stages of the current sheath formation, followed, during the compression, by an energy loss, is examined. Using various values of γ to simulate the effects of energy loss, the variation of beta during the shock phase, and during the isentropic compression phase, is calculated.
The results are compared with observations on a Megajoule Theta pinch and it is shown that the penetration of a few hundred gauss during the sheath formation stage can account for the observed values of beta.
Quasi-linear theory of cherenkov heating of electrons in an inhomogeneous plasma
Authors: Dolgopolov V.V. , Sizonenko V.L. , Stepanov K.N. 
Published: January 2011

The authors investigate, in the quasi-linear approximation, the Cherenkov absorption by plasma electrons of the energy of an electromagnetic field created by external sources. The plasma is in the form of a cylinder of non-uniform radius located in a longitudinal magnetic field and the external sources are specific azimuthal currents flowing in coils surrounding the plasma cylinder. It is assumed that the magnetic pressure significantly exceeds the gas-kinetic pressure of the plasma, that the Larmor radius of the plasma panicles is small compared with the distances within which the plasma density and the electromagnetic field change substantially, that the frequency of the field is significantly less than the electron gyrofrequency, and that the phase velocity is significantly greater than the thermal velocity of the ions, so that thermal motion of the ions can be ignored.
An equation is derived for the diffusion of electrons in velocity space. From this equation it follows that the electron distribution along the velocity component perpendicular to the magnetic field does not change with time and that a plateau is formed on the curve characterizing the dependence of the distribution function on the longitudinal velocity component. The rate of formation of the plateau is different for different values of the velocity component perpendicular to the magnetic field.
In the case of narrow wave packets a diffusion equation is obtained taking Coulomb collisions into account. The slope is found of the curve characterizing the dependence of the background distribution function on the longitudinal velocity component in the steady state, where diffusion on the waves is balanced by collisions.
With narrow wave packets, if the frequency of the external currents coincides with that of the natural oscillations of the plasma cylinder (for a given wave vector value), saturation is reached in the absorption of electromagnetic field energy and, if the amplitudes of the external currents are fairly large, further amplitude increases do not lead to an increase in the absorbed power.
If, however, the external current spectrum contains wave vectors corresponding to the natural oscillations of the plasma cylinder, the formation of a plateau does not lead to absorption saturation (the absorbed power remains proportional to the square of the external current amplitude).
Equilibrium of a plasma pinch in a toroidal constant magnetic field and a helical high-frequency magnetic field
Authors: Gutkin T.I. , Lozovsky S.N. , Boleslavskaya G.I. 
Published: January 2011

The authors consider the equilibrium of a toroidal plasma pinch in a constant magnetic field on which is superposed a helical high-frequency field produced by helical currents flowing on a toroidal surface with major radius R and minor radius rk. The helical currents are proportional to exp[i(ωt – nψ – k‖ζ)], where ω is the frequency imparted by the generator, ψ the polar angle in the meridional cross-section of the torus, and ζ is the length of arc along the major circumference of the torus.
The authors demonstrate that it is possible to achieve equilibrium with high-frequency field pressures less than the kinetic pressure of the plasma.
An expression is derived for the displacement of the pinch in the equilibrium state as a function of high-frequency field amplitude, plasma kinetic pressure, the multipolarity n, and such geometric parameters as the radius of the plasma pinch rp, the radius of the circuit rk and the radius of the torus R.
In the helical high-frequency field, the equilibrium of the plasma pinch depends to a great extent on the strength of the constant magnetic field H0, the plasma concentration N, the frequency of the variable field f = 2π/ω, and the wavelength of the helical current λ‖ = 2π/k‖.
The helical high-frequency electromagnetic field within the plasma is a superposition of two wave types. When H0 < Hcrit = the first type of wave transfers to the skin, and when H0 > Hcrit. it propagates. When k‖rp ≪ 1 and k‖rp ≪ H0/Hcrit. the field of the second type of wave differs only slightly from the vacuum field.
In the region where the first type of wave transfers to the skin, the displacement Δ of the plasma pinch decreases with increasing H0 and becomes zero when H0 = Hres = : with further increases in the magnetic field strength Δ becomes negative. H0 = Hres is the condition for resonance excitation of the helical high-frequency field within the plasma. The most effective use of high-frequency power for equilibrium containment of the plasma pinch within the torus is to be expected near this resonance on the side where Δ > 0.
The change in the sign of Δ is a consequence of a change in the direction of the force acting on the plasma. If there are two types of wave in the plasma, there appear – in addition to the forces associated with the pressure of each individual wave -forces produced by the interaction of the currents excited by one wave type with the field of the other wave type, and vice versa.
For certain parameter values, the phase relations of the fields and currents may be such that the additional forces associated with the cross interaction may work in a direction opposite to that of the forces produced by the pressure of each individual wave.
In the propagation region of the first wave, i.e. where H0 > Hcrit. positive and negative values of the plasma pinch displacement alternate (i.e. there are alternating regions of stable and unstable equilibrium respectively).
Noise in collision-free alkali metal plasmas
Authors: Little P.F. , Middleton C.R. 
Published: January 2011

Oscillations in alkali metal plasmas generated by contact ionization have been attributed to unstable drift waves both in collision-free and collision-dominated plasmas. In the early experiments, however, the influence of the radial electric field Er in causing rotation of the plasma column was ignored. In later work with collisional plasmas, measured Er values were used to calculate frequencies in the rest-frame of the plasma and so demonstrate unstable collisional driftwaves.
Measurements are reported on collision-free potassium and caesium plasmas. The radial electric field causes a Doppler shift comparable with the frequencies observed and often larger than the predicted frequency of the fastest growing drift wave. When this is taken into account the frequencies observed in potassium are within a factor of two of those predicted for the collisionless drift instability and the radial distribution of the density fluctuations shows a peak away from the edge of the column. Other features are consistent with the interpretation of the noise in potassium as due to the drift instability. In caesium edge effects predominate and the cause of the enhanced noise is not the drift instability.
Non-linear theory of Cherenkov excitation of a plasma by a modulated charged-particle beam
Authors: Kurilko V.I. , Ullschmied J. 
Published: January 2011

The authors consider the non-linear problem of the excitation of a plasma resonator by the Cherenkov emission of a density-modulated, injected beam of charged particles. It is assumed that the beam current and the resonator length are small and that the particle energy is large, so that the transit time is small compared with the characteristic field rise time. The modulation frequency is assumed to be equal to one of the natural frequencie s of the resonator. The main non-linear effect is considered to be the reciprocal influence of the excited field on the motion of the beam particles; the plasma is assumed to be linear. The authors derive two non-linear equations of first order which determine in this approximation the time-dependence of the amplitude and phase of the field in the resonator.
The maximum field amplitude and the corresponding phase value are found, and estimates are made of the pulse duration necessary to reach the maximum and of the average beam particle energy losses per pulse.
Thermonuclear future of the Tokamak magnetic confinement device
Authors: Hubert P. 
Published: January 2011

A possible extrapolation of the Tokamak principle towards a thermonuclear reactor raises many problems among which stress is laid on the minimum values required for the equilibrium and stability parameters. Some technological requirements are confronted with the most recent theoretical developments, revealing the existence of a small domain inside of which both points of view may be, perhaps, simultaneously satisfied.
The operation of the reactor would have to be discontinuous but each cycle might conceivably include a plateau lasting about 103 s. A major difficulty arises from the necessity to develop a heating method with an efficiency amounting to at least a few 10−3, keeping in mind other requirements about the uneasy reactor technology.
Methods of determining the density and temperature distribution of a plasma using electromagnetic waves
Authors: Nemov V.V. , Sizonenko V.L. , Stepanov K.N. , Teichmann J. 
Published: January 2011

The authors consider a number of methods of determining the density and temperature distributions along the radius of a plasma cylinder.Determination of the electron density and temperature distributions by measuring the electron cyclotron damping or the phase of an electromagnetic wave passing in a straight line through a plasma cylinder as a function of the “sighting” distance. If the electron velocity distribution is not Maxwellian, additional measurements of the absorption or the phase as a function of the magnetic field or of the angle between the direction of the ray and the magnetic field enable one to find the electron velocity distribution function along the magnetic field at each point in the plasma cylinder.Determination of the plasma density distribution from the fraction of a microwave ray passing through a plasma in a direction perpendicular to the magnetic field, and determination of the effective collision frequency distribution from damping of the intensity of the refracted ray.Determination of the temperature of a plasma in a strong magnetic field from the measured frequency-dependence of the absorption of low-frequency electromagnetic waves under conditions of acoustic resonance.
Genetic Control of a Transition from Black to Straw-White Seed Hull in Rice Domestication
Authors: Zhu Bo-Feng , Si Lizhen , Wang Zixuan , Jingjie Zhu Yan Zhou , Shangguan Yingying , Lu Danfeng , Fan Danlin , Li Canyang , Lin Hongxuan , Qian Qian , Sang Tao , Zhou Bo , Minobe Yuzo , Han Bin 
Published: January 2011

Abstract
The genetic mechanism involved in a transition from the black-colored seed hull of the ancestral wild rice (Oryza rufipogon and Oryza nivara) to the straw-white seed hull of cultivated rice (Oryza sativa) during grain ripening remains unknown. We report that the black hull of O. rufipogon was controlled by the Black hull4 (Bh4) gene, which was fine-mapped to an 8.8-kb region on rice chromosome 4 using a cross between O. rufipogon W1943 (black hull) and O. sativa indica cv Guangluai 4 (straw-white hull). Bh4 encodes an amino acid transporter. A 22-bp deletion within exon 3 of the bh4 variant disrupted the Bh4 function, leading to the straw-white hull in cultivated rice. Transgenic study indicated that Bh4 could restore the black pigment on hulls in cv Guangluai 4 and Kasalath. Bh4 sequence alignment of all taxa with the outgroup Oryza barthii showed that the wild rice maintained comparable levels of nucleotide diversity that were about 70 times higher than those in the cultivated rice. The results from the maximum likelihood Hudson-Kreitman-Aguade test suggested that the significant reduction in nucleotide diversity in rice cultivars could be caused by artificial selection. We propose that the straw-white hull was selected as an important visual phenotype of nonshattered grains during rice domestication.