bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitromatrix provides improved LC‐MALDI signals and more protein identifications
Authors: Kouvonen Petri , McDonnell Liam A. , Heeren Ron M. A. , Corthals Garry L. 
Published: March 2009

AbstractThe beneficial use of NC in MALDI‐MS has previously been reported to provide better S/N and reproducibility as well as less alkali metal adducts. We have therefore investigated if additional beneficial properties of NC also existed for commonly employed proteomics‐based LC‐MALDI procedures. Specifically we studied the effects of NC as a matrix cofactor for prestructured sample supports (AnchorChip plates), and compared the performance with several alternative sample preparation methods recently reported in the literature. The work reported here describes a new method of mixing the NC‐matrix solution with the LC‐eluent prior to sample deposition and shows that a mixture of CHCA and NC in a complex solvent offers superior analytical results in several ways: most striking is the higher signal intensity, and that the signals last much longer, due to the robustness of the matrix formulation. We have tested the use of the nitromatrix on a single LC‐MALDI preparation and found that at least ten reiterative analyses could be performed, resulting in total analysis times of more than 75 h (approximately 15 million laser shots). Consequently more than twice as many proteins could be identified than from a single analysis. This combination of longer, and stronger, MALDI signals provided an increase in the number of peptides, greater sequence coverage in MS/MS experiments and ultimately more confident peptide assignments.
Plasma‐Polymerization of HMDSO Using an Atmospheric Pressure Dielectric Barrier Discharge
Authors: Morent Rino , De Geyter Nathalie , Jacobs Tinneke , Van Vlierberghe Sandra , Dubruel Peter , Leys Christophe , Schacht Etienne 
Published: March 2009

AbstractIn this work, an atmospheric pressure glow‐like dielectric barrier discharge in argon with small admixtures of hexamethyldisiloxane (HMDSO) is employed for the deposition of thin polydimethylsiloxane (PDMS) films. The effect of discharge power and feed composition (monomer concentration) on film properties has been investigated by means of contact angle measurements, Fourier‐Transform Infrared Spectroscopy (FT‐IR), and Atomic Force Microscopy (AFM). The results are described by defining a W/FM value, where W is the discharge power, F the monomer flow rate, and M is the molecular weight of the monomer. This paper shows that the deposition rate and the chemical composition of the deposited films are strongly affected by the W/FM value at which plasma‐polymerization is performed.
Persistent proteomic alterations in the medial prefrontal cortex with abstinence from cocaine self‐administration
Authors: Lull Melinda E. , Erwin Mandi S. , Morgan Drake , Roberts David C. S. , Vrana Kent E. , Freeman Willard M. 
Published: March 2009

AbstractNeuroproteomic studies of drug abuse offer the potential for a systems‐level understanding of addiction. Understanding cocaine‐responsive alterations in brain protein expression that persist even with extended abstinence may provide insight into relapse liability. In the current study, protein changes in the medial prefrontal cortex of cocaine self‐administering rats following 1 and 100 days of enforced abstinence were quantified by 2‐D DIGE. We have previously reported increased drug‐seeking and drug‐taking, as well as mRNA and epigenetic changes in this model even after 100 days of enforced abstinence. A number of statistically significant changes in proteins relating to synapse function and neuronal remodeling were evident, including neurofilament medium and Hsp73, which increased at 1 day of abstinence, but returned to normal levels following 100 days of abstinence. Dynamin‐1 and synaptosome‐associated protein 25 kDa (SNAP‐25) were unchanged at 1 day of abstinence, but were significantly decreased after 100 days. These data demonstrate that while some protein changes return to normal levels following enforced cocaine abstinence, a number remain or become altered after long periods, up to 100 days, of cocaine abstinence. Those protein expression changes that do not reset to pre‐cocaine exposure levels may contribute to the persistent relapse potential that occurs in response to cocaine abstinence.
Non‐DMS related ferromagnetism in transition metal doped zinc oxide
Authors: Potzger Kay , Zhou Shengqiang 
Published: March 2009

AbstractWe review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can easily be confused with the formation of a ferromagnetic diluted magnetic semiconductor (DMS). We will focus on metallic as well as oxide precipitates and the difficulties of their identification. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large predators and biogeochemical hotspots: brown bear (Ursus arctos) predation on salmon alters nitrogen cycling in riparian soils
Authors: Holtgrieve Gordon W. , Schindler Daniel E. , Jewett Peter K. 
Published: March 2009

AbstractTwo important themes in ecology include the understanding of how interactions among species control ecosystem processes, and how habitats can be connected through transfers of nutrients and energy by mobile organisms. An impressive example of both is the large influx of nutrients and organic matter that anadromous salmon supply to inland aquatic and terrestrial ecosystems and the role of predation by brown bears (Ursus arctos) in transferring these marine‐derived nutrients (MDN) from freshwater to riparian habitats. In spite of the recognition that salmon‐bear interactions likely play an important role in controlling the flux of MDN from aquatic to riparian habitats, few studies have linked bear predation on salmon to processes such as nitrogen (N) or carbon (C) cycling. We combine landscape‐level survey data and a replicated bear‐exclosure experiment to test how bear foraging on salmon affects nitrous oxide (N2O) flux, carbon dioxide (CO2) flux, and nutrient concentrations of riparian soils. Our results show that bears feeding on salmon increased soil ammonium (NH4+) concentrations three‐fold and N2O flux by 32‐fold. Soil CO2 flux, nitrate (NO3−), and N transformation differences were negligible in areas where bears fed on salmon. Reference areas without concentrated bear activity showed no detectable change in soil N cycling after the arrival of salmon to streams. Exclosure experiments showed that bear effects on soil nutrient cycles were transient, and soil N processing returned to background conditions within 1 year after bears were removed from the system. These results suggest that recipient ecosystems do not show uniform responses to MDN inputs and highlight the importance of large mobile consumers in generating landscape heterogeneity in nutrient cycles.
CYP46A1variants influence Alzheimer’s disease risk and brain cholesterol metabolism
Authors: Kölsch Heike , Lütjohann Dieter , Jessen Frank , Popp Julius , Hentschel Frank , Kelemen Peter , Schmitz Sandra , Maier Wolfgang , Heun Reinhard 
Published: March 2009

AbstractBackgroundCholesterol 24S-hydroxylase (CYP46) catalyzes the conversion of cholesterol to 24S-hydroxycholesterol, the primary cerebral cholesterol elimination product. Only few gene variations in CYP46 gene (CYP46A1) have been investigated for their relevance as genetic risk factors of Alzheimer’s disease (AD) and results are contradictory.MethodsWe performed a gene variability screening inCYP46A1and investigated the effect of gene variants on the risk of AD and on CSF levels of cholesterol and 24S-hydroxycholesterol.ResultsTwo of the identified 16 SNPs inCYP46A1influenced AD risk in our study (rs7157609:p= 0.016; rs4900442:p= 0.019). The interaction term of both SNPs was also associated with an increased risk of AD (p= 0.006). Haplotypes including both SNPs were calculated and haplotype G–C was identified to influence the risk of AD (p= 0.005). AD patients and non-demented controls, who were carriers of the G–C haplotype, presented with reduced CSF levels of 24S-hydroxycholesterol (p= 0.001) and cholesterol (p< 0.001).ConclusionOur results suggest thatCYP46A1gene variations might act as risk factor for AD via an influence on brain cholesterol metabolism.
Gas-ionizing shocks in a magnetic field
Authors: Cowley M. D. 
Published: March 2009

Ionizing shocks for plane flows with the magnetic field lying in the flow plane are considered. The gas is assumed to be electrically conducting downstream, but non-conducting upstream. Shocks whose downstream state has a normal velocity component less than the slow magneto-acoustic-wave speed and whose upstream state is supersonic are found to be non-evolutionary in the face of plane magneto-acoustic disturbances, unless the upstream electric field in a frame of reference where the gas is at rest is arbitrary. Velocity conditions are also determined for shock stability with the electric field not arbitrary.Shock structures are found for the case of large ohmic diffusion, the initial temperature rise and ionization of the gas being caused by a thin transition having the properties of an ordinary gasdynamic shock. For the case where shocks are evolutionary when the upstream electric field is arbitrary, the shock structure requirements only restrict the electric field by limiting the range of possible values. When shocks are evolutionary with the electric field not arbitrary, they can only have a structure for a particular value of the electric field. Limits to the current carried by ionizing shocks and the effects of precursor ionization are discussed qualitatively.
Relativistic formulation for non-linear waves in a non-uniform plasma
Authors: Butler D. S. , Gribben R. J. 
Published: March 2009

The mathematical formulation for the problem of non-linear oscillations in a self-consistent, non-uniform, collisionless plasma is considered. The fully nonlinear treatment illuminates the effect of the wave on the background distribution of the plasma through which it is passing. It is assumed that, although the overall non-uniformity may be large, significant changes occur only over time or length scales which are large compared with the plasma period or Debye length respectively. Exclusion of secular terms from the solution leads to a Liouvile type equation, which must be satisfied by the background distribution, and to propagation laws for the waves.The theory is restricted to almost one-dimensional electrostatic waves and a general presentation is given from a relativistically-invariant point of view. Then the equations are derived in terms of physical variables for the special case in which: (i) the distribution functions and electrostatic potential depend on one space co-ordinate (that of propagation of the wave) and the former on the corresponding particle velocity component only, (ii) the wave is slowly-varying only with respect to this co-ordinate and time, and (iii) the magnetic field is zero. Finally, the non-relativistic limit of this case is considered in more detail. The boundary conditions satisfied by the distribution functions are discussed and this leads to the conclusion that in some circumstances thin sheets of probability fluid are formed in phase space and the background distribution cannot be strictly defined. This motivates a reformulation and subsequent re-solution of the problem (for this non-relativistic special case) in terms of weak functions, corresponding to the physical assumption of the presence of a small-scale mixing mechanism, which is excited by and smears the sheeted distribution but is otherwise dormant.The results of the investigation are given as a system of differentio-integral equations which must be solved if necessary conditions for the absence of nonsecular solutions (of the Vlasov and Maxwell equations) are to be satisfied. No solution of this system is attempted here.
Transverse instabilities in a collisionless plasma
Authors: Smith A. 
Published: March 2009

Transverse instabilities in an electron gas with a neutralizing background, in the absence of a permanent magnetic field are discussed, mostly when the equilibrium velocity distribution is slightly spheroidal, i.e. of the formwith α ˜ γ and with the functional form of f0 not given explicitly. It is found that two types of unstable waves exist; one grows at a rate proportional to ε½‖ cos θ‖3 whenever ε > 0, the other at a rate proportional to(ε cos2θ)½ whenever ε cos 2θ > 0, where ε = (γ2/α2) — 1, and θ is the angle the wave vector makes with the axis of symmetry of the velocity spheroid. It is shown that within the approximation we are working the complex phase velocity is pure imaginary, i.e. the unstable waves are standing waves. The effect of a small permanent magnetic field is considered. The phase velocity becomes complex, at least for propagation parallel to the magnetic field and the instability rate decreases by a factor where H0 is the permanent magnetic field and 〈H2〉½ the r.m.s. maximum field that grows before non-linear effects take over. The maximum instability rate is compared with the collision rate and is found to be higher in low density, high temperature plasmas such as the solar wind. An application to collisionless shock theory is suggested.
Hot plasma theory of whistler mode wave packet propagation along a non-uniform magnetic field
Authors: Houghton M. J. 
Published: March 2009

We discuss the propagation of wave packets of the formin an infinite uniform plasma, where G(z, t) is a slowly varying function of space z and time t. One can very simply derive the equation of change of G(z, t) for the stable or unstable case. The terms in the equation are of physical interest and clearly define the limitations of linear theory. We then investigate the problem of whistler mode wave propagation in a collisionless Vlasov plasma in a given non-uniform magnetic field. We choose the electric field to be of a W.K.B. form and the particle distribution to be isotropic. We can express the perturbation in the particle distribution in terms of an integration along the zero-order par tide orbits (an integration overtime). These orbits can be found correct to a term linear in a smallness parameter ε (when ε equals zero we arrive back at a uniform magnetic field). The charge and current density due to the perturbation are related through Maxwell's equations to the electric and magnetic field of the wave in the usual self consistent Boltzmann—Vlasov description. We show that the contribution to the current arises from recent events in the history of a given particle because of the finite temperature of the plasma. This result leads to an expansion of slowly varying parameters which in turn gives rise to the equation governing the motion of the wave packet.
Relativistic effects on non-linear waves in a cold collisionless plasma
Authors: Inoue Yoshinori 
Published: March 2009

Non-linear periodic waves propagating across a magnetic field are investigated, taking relativistic effects into account. The governing equations of the phenomena are taken to be the relativistic two-fluid plasma equations for a cold plasma together with Maxwell's equations. The analytical solution in the non-relativistic case was obtained by Adlam and Allen and others, a case where the quasi- neutral approximation is a good one and the inertia of the electrons plays an essential role in the dispersion effect of the plasma.In contrast, the analysis of the relativistic waves shows that the quasi- neutral approximation becomes invalid and that the charge separation plays an essential role in the dispersion effect while the inertia of the electrons plays minor role only. Therefore the phenomena to be investigated have a length scale of the appropriately defined Debye distance (the ion Larmor radius), while in the non-relativistic case the width of the wave is of the order of the geometric mean of the Larmor radii of the electrons and of the ions. In the present case where the electron mass may be neglected, there exists an exact solution which is a good approximation for a real plasma. The solitary wave solution is found as the limiting case of infinite periodicity.
Asymptotic matching of plasma and sheath in an active low pressure discharge
Authors: Franklin R. N. , Ockendon J. R. 
Published: March 2009

The method of matched asymptotic expansions is applied to the fluid model of the low-pressure positive column. The expansion of the eigenvalue in the plasma balance equation is obtained to second order in plane and in cylindrical geometry, and uniformly valid expressions for charged particle densities and fluid velocity in two separate regions are indicated.The free-fall model is also examined and the scales of the transition layer and sheath layer found. Comparison is made with the results of direct numerical integration of the equations involved for both models.
Generalized theory of the stabifity of shock waves in magnetogasdynamics
Authors: Woods L. C. 
Published: March 2009

Stability of MGD shock waves can be investigated either by disturbing the shock discontinuity by incident waves and then considering whether the response of the shock is unique and determinate or not, or by studying the behaviour of the dissipative shock structure with variations in the magnitudes of the dissipations. Both approaches yield the same results, which appears at first sight to be a coincidence. In this paper we show, from a single treatment that includes each as special cases, why the two methods yield the same conclusions.Also, by including the Hall term on Ohm's law, we are able to resolve the uncertainty about the stability of switch-on and switch-off shocks that occurs in the usual MHD treatment of the problem. Finally, it is shown that the Hall term also introduces the possibility of electric field layers in the unsteady shock and thereby reduces the number of shock boundary conditions. This throws some doubt on the value of the wave-interaction theory for shocks in real plasmas.
Corrigendum
Authors: Bhatia P. K. 
Published: March 2009

‘On effects of neutral gas friction and ion viscosity on the Rayleigh-Taylor instability of a stratified plasma in the presence of Hall currents’By P. K. Bhatia,J. Plasma Phys. vol. 11, 1974, pp. 1–10Bhatia (1974) investigated the effects of neutral gas friction and ion viscosity on the dynamical stability of a composite plasma of variable density in the presence of the effects of Hall currents.
Turbulent excitation of spontaneous reconnection
Authors: Deeds D. , Van Hoven G. 
Published: March 2009

We explore the long-term nonlinear evolution of a tearing-mode-unstable sheared-field plasma in a turbulent environment. Two different physical configurations are modeled, and a different computational system is used for each. Results of both sets of calculations show that magnetic tearing arises spontaneously provided that the initial turbulence energy level is below the natural saturation level of the tearing instability.We discuss briefly the relationship between our results and those of previous calculations, concluding that there are no significant unexplainable disagreements.
Parametric instabifity of transverse and Langmuir waves in a plasma
Authors: Lee Kai Fong 
Published: March 2009

The parametric excitation of transverse and Langmuir waves by an externally-driven electromagnetic field of frequency (ω0 > 2ωp) in a warm and collisional plasma is studied, using the fluid equations. By an application of the multiple- time-scale perturbation method, the threshold intensity and the growth rate above threshold are obtained. The results are compared with those of Goldman (1969) and Prasad (1968), both of whom worked with a kinetic model.The theory of parametric instabilities in plasmas has been the subject of numerous investigations in recent years. Broadly speaking, the instabilities can be grouped into two categories: those for which the excited waves are purely electrostatic (see e.g. DuBois & Goldman 1965, 1967; Silin 1965; Lee & Su 1966; Jackson 1967; Nishikawa 1968; Kaw & Dawson 1969; Tzoar 1969; Sanmartin 1970; McBride 1970; Perkins & Flick 1971; Fejer & Leer 1972a, b; Bezzerides & Weinstock 1972; DuBois & Goldman 1972), and those for which one of the excited waves is electromagnetic (see e.g. Goldman & Dubois 1965; Montgomery & Alexeff 1966; Chen & Lewak 1970; Bodner & Eddleman 1972; Fejer & Leer 1972b; Lee & Kaw 1972; Forslund et al. 1972).
Analysis of a generalized nonlinear diffusion equation in fusion plasma physics
Authors: Anderson D. , Lisak M. 
Published: March 2009

Using similarity methods, an investigation is made of a generalized nonlinear diffusion equation arising in plasma physics in connexion with several recently proposed models for turbulent plasma energy transport and particle diffusion.In almost every field of physics, diffusion or transport equations of the form Ψt = Δ. (DΔΨ) play an important role. The theory of linear diffusion equations, where the diffusion constant D is independent of Ψ, has been developed to a high degree of sophistication (e.g. Carsiaw & Jaeger 1959).
Wake field in electron–positron plasmas
Authors: Avinash K. , Berezhiani V. I. 
Published: March 2009

SummaryWe have studied the possibility of exciting a wake field in an electron–positron plasma by the injection of relativistic electron bunches. We have investigated the change in frequency of electronmagnetic radiation propagating through the resulting inhomogeneity. Our main conclusion is that it is not necessary to invoke a magnetic field in order to excite a wake field in an electron–positron plasma. As shown here, the necessary charge separation could come from the injection of energetic particle bunches. This mechanism of wake-field creation and subsequent particle/photon acceleration could operate in a pulsar magnetosphere, where particle bunches are extracted energetically from the pulsar surface. For example, pulsar radio emissions exhibit ultra-short intensity variations within individual pulses with time scales ranging from 1 μs to 1 ms (Cordes 1979). Several authors have proposed (Chian & Kennel 1983; Mofiz, De Angelis & Forlani 1985; Mikhailovskii, Onishchenko & Tatarinov 1985) that these pulsations can be explained as being due to soliton formation in the pulsar magnetosphere.We believe that these micropulsations can also be explained by modulation of the radiation caused by the wake field. In order to have a quantitative estimation, we need to take into account the effects of thermal motion of particles as well as plasma inhomogeneity, etc. The present results should also be useful for understanding nonolinear photon motion in cosmic plasmas, such as those found in the early universe and in active galactic nuclei (Tajima & Taniuti 1990).