129 research outputs found
General formulation of interactions and energy loss of particles in plasmas: Quantum-wave-packet model versus a semiclassical approach
In this work we present a general quantum-mechanical and statistical formulation of the process of interactions of external test particles with plasmas, considering the calculation of the energy-loss coefficients, including energy losses, mean-free paths, and straggling, and describing in detail the differences between protons, positrons, and electrons. Two relevant aspects contained in this formulation are studied: the competing action of loss and gain processes in the interaction with the plasma, and the role of thermal fluctuations in those interactions. We propose two different approaches to evaluate processes of electronic interactions in plasmas. To formulate the first approach we introduce modifications to the quantum-wave-packet dielectric method, which provides a reliable description over wide ranges of plasma densities and temperatures as compared with full quantum-mechanical dielectric theory. The second approach is a semiclassical dielectric method. It consists of including statistical quantum distributions and restrictions in the energy-loss expression, combined with the classical dielectric function for hot plasmas obtained from the linearized Vlasov-Poisson equation. We compare the results from both methods on an extensive range of parameters that include low, intermediate, and high energies, with densities and temperatures going from normal laboratory conditions to very high values, such as those of interest for studies on inertial fusion, Tokamak plasmas, and astrophysical media. We give also special consideration to the case of electrons, where the restrictions imposed by the identity with plasma electrons produce important effects.Fil: Archubi, Claudio DarĂo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de AstronomĂa y FĂsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomĂa y FĂsica del Espacio; ArgentinaFil: Arista, N. R.. ComisiĂłn Nacional de EnergĂa AtĂłmica. Centro AtĂłmico Bariloche; Argentin
Dicluster Stopping in a Degenerate Electron Gas
In this paper we report on our theoretical studies of various aspects of the
correlated stopping power of two point-like ions (a dicluster) moving in close
but variable vicinity of each other in some metallic target materials the
latter being modelled by a degenerate electron gas with appropriate densities.
Within the linear response theory we have made a comprehensive investigation of
correlated stopping power, vicinage function and related quantities for a
diproton cluster in two metallic targets, aluminum and copper, and present
detailed and comparative results for three approximations to the electron gas
dielectric function, namely the plasmon-pole approximation without and with
dispersion as well as with the random phase approximation. The results are also
compared, wherever applicable, with those for an individual projectile.Comment: 29 figures, LaTe
Dielectric approaches for interactions of protons, positrons, and electrons in cold matter and plasmas
This work investigates the projectile and temperature dependence of the energy loss of charged particles in matter. To this end, we analyze two dielectric approaches which consider the presence of bound and free electrons and the effects of the ionization process. With these approaches, we calculate the energy-loss moments of protons, positrons, and electrons traversing Si, Fe, and Al targets, both in the cold solid phase and in the plasma state. We compare the results from the unified-wave-packet model (UWPM) and the shellwise local plasma approximation (SLPA) on an extensive range of parameters, including low, intermediate, and high projectile energies and target temperatures going from cold solid-state densities to hot plasma with temperatures up to 1000 eV. We reformulate the SLPA to include light-particle restrictions. We give special consideration to the case of positrons and electrons, where the inner-shell effects have not been analyzed in our previous works. Comparisons with experimental results for cold solid targets are presented, and stopping enhancement effects for heated targets are described, showing the physical origin of these effects.Fil: Archubi, Claudio DarĂo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de AstronomĂa y FĂsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomĂa y FĂsica del Espacio; ArgentinaFil: Montanari, Claudia Carmen. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de AstronomĂa y FĂsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomĂa y FĂsica del Espacio; ArgentinaFil: Arista, N. R.. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Ărea de EnergĂa Nuclear. Instituto Balseiro. Archivo HistĂłrico del Centro AtĂłmico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo HistĂłrico del Centro AtĂłmico Bariloche e Instituto Balseiro; Argentin
Interference in the plasmon field excited by a diatomic molecule on metallic cylindrical nanostructures
n/
The role of E1-E2 interplay in multiphonon Coulomb excitation
In this work we study the problem of a charged particle, bound in a
harmonic-oscillator potential, being excited by the Coulomb field from a fast
charged projectile. Based on a classical solution to the problem and using the
squeezed-state formalism we are able to treat exactly both dipole and
quadrupole Coulomb field components. Addressing various transition amplitudes
and processes of multiphonon excitation we study different aspects resulting
from the interplay between E1 and E2 fields, ranging from classical dynamic
polarization effects to questions of quantum interference. We compare exact
calculations with approximate methods. Results of this work and the formalism
we present can be useful in studies of nuclear reaction physics and in atomic
stopping theory.Comment: 10 pages, 6 figure
Breeding systems of floral colour forms in the Drosera cistiflora species complex
The study was supported by the National Research Foundation of South Africa (Grant 46372 to SDJ).Variation in plant breeding systems has implications for pollinatorâmediated selection on floral traits and the ecology of populations. Here we evaluate pollinator contribution to seed production, selfâcompatibility and pollen limitation in different floral colour forms of Drosera cistiflora sensu lato (Droseraceae). These insectivorous perennial plants are endemic to fynbos and renosterveld vegetation in the Cape Floristic Region of South Africa, and the species complex includes five floral colour forms (pink, purple, red, white and yellow), some of which are known to be pollinated by beetles. Controlled handâpollination experiments were conducted in 15 populations of D. cistiflora s.l. (two to four populations per floral colour form) to test whether the colour forms vary in their degree of selfâcompatibility and their ability to produce seeds through autonomous selfâfertilization. Yellowâflowered forms were highly selfâincompatible, while other floral colour forms exhibited partial selfâcompatibility. Seed set resulting from autonomous selfing was very low, and pollinator dependence indices were high in all populations. Since hand crossâpollination resulted in greater seed set than open pollination in 13 of the 15 populations, we inferred that seed production is generally pollenâlimited.Drosera cistiflora s.l. typically exhibits high levels of pollinator dependence and pollen limitation. This is unusual among Drosera species worldwide and suggests that pollinators are likely to mediate strong selection on attractive traits such as floral colour and size in D. cistiflora s.l. These results also suggest that the floral colour forms of D. cistiflora s.l. which are rare and threatened are likely to be vulnerable to local extinction if mutualisms were to collapse indefinitely.PostprintPeer reviewe
Health and economic impact of rotavirus vaccination in GAVI-eligible countries
<p>Abstract</p> <p>Background</p> <p>Rotavirus infection is responsible for about 500,000 deaths annually, and the disease burden is disproportionately borne by children in low-income countries. Recently the World Health Organization (WHO) has released a global recommendation that all countries include infant rotavirus vaccination in their national immunization programs. Our objective was to provide information on the expected health, economic and financial consequences of rotavirus vaccines in the 72 GAVI support-eligible countries.</p> <p>Methods</p> <p>We synthesized population-level data from various sources (primarily from global-level databases) for the 72 countries eligible for the support by the GAVI Alliance (GAVI-eligible countries) in order to estimate the health and economic impact associated with rotavirus vaccination programs. The primary outcome measure was incremental cost (in 2005 international dollars [I25 per vaccinated child (~200 was 47. Using the WHO's cost-effectiveness threshold based on per capita GDP, the vaccines were considered cost-effective in 68 of the 72 countries (~94%). A 10-year routine rotavirus vaccination would prevent 0.9-2.8 million rotavirus associated deaths among children under age 5 in the poorest parts of the world, depending on vaccine scale-up scenarios. Over the same intervention period, rotavirus vaccination programs would also prevent 4.5-13.3 million estimated cases of hospitalization and 41-107 million cases of outpatient clinic visits in the same population.</p> <p>Conclusions</p> <p>Our findings suggest that rotavirus vaccination would be considered a worthwhile investment for improving general development as well as childhood health level in most low-income countries, with a favorable cost-effectiveness profile even under a vaccine price (5.0 per dose) higher than those of traditional childhood vaccines.</p
Stopping of relativistic projectiles in two-component plasmas
Relativistic and correlation contributions to the polarizational energy losses of heavy
projectiles moving in dense two-component plasmas are analyzed within the method of moments
that allows one to reconstruct the Lindhard loss function from its three independently known power
frequency moments. The techniques employed result in a thorough separation of the relativistic
and correlation corrections to the classical asymptotic form for the polarizational losses obtained
by Bethe and Larkin. The above corrections are studied numerically at different values of plasma
parameters to show that the relativistic contribution enhances only slightly the corresponding
value of the stopping power.This research was financially supported by the Spanish Ministerio de Educacion y Ciencia Project No. ENE2010-21116-C02-02 and by the Science Committee of the Ministry of Education and Sciences of the Republic of Kazakhstan under Grants No. 1128/GF, 1129/GF and 1099/GF. IMT acknowledges the hospitality of the al-Farabi Kazakh National University.Arkhipov, YV.; Ashikbayeva, AB.; Askaruly, A.; Davletov, AE.; Tkachenko Gorski, IM. (2013). Stopping of relativistic projectiles in two-component plasmas. EPL. 104(3):35003-p1-35003-p6. https://doi.org/10.1209/0295-5075/104/35003S35003-p135003-p6104
Biodiversity and ecosystem services in the Campo Rupestre: a road map for the sustainability of the hottest Brazilian biodiversity hotspot.
- âŠ