Modulational instability of dust acoustic waves in dusty plasmas: Modulation obliqueness, background ion nonthermality, and dust charging effects

The oblique modulational instability of dust acoustic (DA) waves in an unmagnetized warm dusty plasma with nonthermal ions, taking into account dust grain charge variation (charging), is investigated. A nonlinear Schrodinger-type equation governing the slow modulation of the wave amplitude is derived. The effects of dust temperature, dust charge variation, ion deviation from Maxwellian equilibrium (nonthermality) and constituent species' concentration on the modulational instability of DA waves are examined. It is found that these parameters modify significantly the oblique modulational instability domain in the k-theta plane. Explicit expressions for the instability rate and threshold have been obtained in terms of the dispersion laws of the system. The possibility and conditions for the existence of different types of localized excitations are also discussed. The findings of this investigation may be useful in understanding the stable electrostatic wave packet acceleration mechanisms close to the Moon, and also enhances our knowledge on the occurrence of instability associated to pickup ions around unmagnetized bodies, such as comets, Mars, and Venus.

Oblique modulation of electrostatic modes and envelope excitations in pair-ion and electron-positron plasmas

The nonlinear amplitude modulation of electrostatic waves propagating in a collisionless two-component plasma consisting of negative and positive species of equal mass and absolute charge is investigated. Pair-ion (e.g., fullerene) and electron-positron (e-p) plasmas (neglecting recombination) are covered by this description. Amplitude perturbation oblique to the direction of propagation of the wave has been considered. Two distinct linear electrostatic modes exist, namely an acoustic lower mode and Langmuir-type optic-type upper one. The behavior of each of these modes is examined from the modulational stability point of view. The stability criteria are investigated, depending on the electrostatic carrier wave number, the angle theta between the modulation and propagation directions, and the positron-to-electron temperature ratio sigma. The analysis shows that modulated electrostatic wavepackets associated to the lower (acoustic) mode are unstable, for small values of carrier wave number k (i.e., for large wavelength lambda) and for finite (small) values of the angle theta (yet stable for higher theta), while those related to the upper (optic-like) mode are stable for large values of the angle theta only, in the same limit, yet nearly for all values of sigma. These results are of relevance in astrophysical contexts (e.g., in pulsar environments), where e-p plasmas are encountered, or in pair fullerene-ion plasmas, in laboratory. (c) 2006 American Institute of Physics.

Dust-acoustic wave modulation in the presence of superthermal ions

A study is presented of the nonlinear self-modulation of low-frequency electrostatic (dust acoustic) waves propagating in a dusty plasma, in the presence of a superthermal ion (and Maxwellian electron) background. A kappa-type superthermal distribution is assumed for the ion component, accounting for an arbitrary deviation from Maxwellian equilibrium, parametrized via a real parameter kappa. The ordinary Maxwellian-background case is recovered for kappa ->infinity. By employing a multiple scales technique, a nonlinear Schrodinger-type equation (NLSE) is derived for the electric potential wave amplitude. Both dispersion and nonlinearity coefficients of the NLSE are explicit functions of the carrier wavenumber and of relevant physical parameters (background species density and temperature, as well as nonthermality, via kappa). The influence of plasma background superthermality on the growth rate of the modulational instability is discussed. The superthermal feature appears to control the occurrence of modulational instability, since the instability window is strongly modified. Localized wavepackets in the form of either bright-or dark-type envelope solitons, modeling envelope pulses or electric potential holes (voids), respectively, may occur. A parametric investigation indicates that the structural characteristics of these envelope excitations (width, amplitude) are affected by superthermality, as well as by relevant plasma parameters (dust concentration, ion temperature).

Nonlinear modulation of ion-acoustic waves in two-electron-temperature plasmas

The amplitude modulation of ion-acoustic waves IS investigated in a plasma consisting of adiabatic warm ions, and two different populations of thermal electrons at different temperatures. The fluid equations are reduced to nonlinear Schrodinger equation by employing a multi-scale perturbation technique. A linear stability analysis for the wave packet amplitude reveals that long wavelengths are always stable, while modulational instability sets in for shorter wavelengths. It is shown that increasing the value of the hot-to-cold electron temperature ratio (mu), for a given value of the hot-to-cold electron density ratio (nu): favors instability. The role of the ion temperature is also discussed. In the limiting case nu = 0 (or nu -> infinity). which correspond(s) to an ordinary (single) electron-ion plasma, the results of previous works are recovered.

Apc(MIN) modulation of vitamin D secosteroid growth control

A central paradox of vitamin D biology is that 1alpha,25-(OH)(2) D(3) exposure inversely relates to colorectal cancer (CRC) risk despite a capacity for activation of both pro- and anti-oncogenic mediators including osteopontin (OPN)/CD44 and E-cadherin, respectively. Most sporadic CRCs arise from adenomatous polyposis coli (APC) gene mutation but understanding of its effects on vitamin D growth control is limited. Here we investigate effects of the Apc(Min/+) genotype on 1alpha,25-(OH)(2) D(3) regulation of OPN/CD44/E-cadherin signalling and intestinal tumourigenesis, in vivo. In untreated Apc(Min/+) versus Apc(+/+) intestines, expression levels of OPN and its CD44 receptor were increased, whereas E-cadherin tumour suppressor signalling was attenuated. Treatment by 1alpha,25-(OH)(2) D(3) or rationally designed analogues (QW or BTW) enhanced OPN but inhibited expression of CD44, the OPN receptor implicated in cell growth. These treatments also enhanced E-cadherin tumour suppressor activity, characterized by inhibition of beta-catenin nuclear localization, T-cell factor 1 and c-myelocytomatosis protein expression in Apc(Min/+) intestine. All secosteroids suppressed Apc(Min/+)-driven tumourigenesis although QW and BTW had lower calcium-related toxicity. Taken together, these data indicate that the Apc(Min/+) genotype modulates vitamin D secosteroid actions to promote functional predominance of E-cadherin tumour suppressor activity within antagonistic molecular networks. APC heterozygosity may promote favourable tissue- or tumour-specific conditions for growth control by vitamin D secosteroid treatment.

Peroxiredoxin: a central player in immune modulation:a central player in immune modulation

Peroxiredoxins (Prx) are a family of anti-oxidants that protect cells from metabolically produced reactive oxygen species (ROS). The presence of these enzymes in the secretomes of many parasitic helminths suggests they provide protection against ROS released by host immune effector cells. However, we recently reported that helminth-secreted Prx also contribute to the development of Th2-responses via a mechanism involving the induction of alternatively activated macrophages. In this review, we discuss the role helminth Prx may play in modulating the immune responses of their hosts.

Simultaneous optical and X-ray observations of flares and rotational modulation on the RS CVn binary HR 1099 (V711 Tau) from the MUSICOS 1998 campaign

We present simultaneous and continuous observations of the Halpha, Hbeta, He I D-3, Na I D-1,D-2 doublet and the Ca II H&K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of 2.(d)8. Two large optical flares were observed, both showing an increase in the emission of Halpha, Ca II H K, Hbeta and He I D-3 and a strong filling-in of the Na I D-1, D-2 doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Halpha and He I D-3 in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5 V star was in front. A possible periodicity in the X-ray flare-like events was also found.

Measurements of relativistic self-phase-modulation in plasma

We report the first systematic observations of relativistic self-phase-modulation (RSPM) due to the interaction of a high intensity laser pulse with plasma. The plasma was produced in front of a solid target by the prepulse of a 100 TW laser beam. RSPM was observed by monitoring the spectrum of the harmonics generated by the intense laser pulse during the interaction. The multipeaked broadened spectral structure produced by RSPM was studied in plasmas with different density scale lengths for laser interactions at intensities up to 3.0x1019 W cm(-2) (a=p(osc)/m(e)c=4.7). The results are compared with calculated spectra and agreement is obtained.

Nematode neuropeptide modulation of the vagina vera of Ascaris suum: in vitro effects of PF1, PF2, PF4, AF3 and AF4

Ascaris suum possesses a large number of FMRFamide-related peptides (FaRPs) of which KNEFIRFamide (AF1), KHEYLRFamide (AF2) and KSAYMRFamide (AF8/PF3) have been shown to modulate the intrinsic, rhythmic activity of the vagina vera of A. suum in vitro. In the present study, the effects of the nematode FaRPs, SDPNFLRFamide (PF1), SADPNFLREamide (PF2) and KPNFIRFamide (PF4) (from Panagrellus redivivus) and AVPGVLRFamide (AF3) and GDVPGVLRFamide (AF4) (from A. suum) on the in vitro activity of the vagina vera were examined. The effects of each of the peptides were qualitatively and quantitatively distinct. All 3 FaRPs from P. redivivus were inhibitory, causing a cessation of contractions. PF2 was 3 times more potent than PF1, with a threshold of 1 nM. Although PF4 was the least potent (threshold, 10 nM), its effects at greater than or equal to 10 nM were quantitatively the greatest. Both AF3 and AF4 (1 mu M) induced complex, multiphasic responses consisting of an initial contraction and spastic paralysis followed by a return of contractile activity of increased amplitude. AF3 was 3 times more potent than AF4. The effects of these peptides had some similarities to those observed on A. suum somatic body wall muscle in vitro, with PF1, PF2 and PF4 being inhibitory and AF3 and AF4 being excitatory.