6,661 research outputs found
Parametric Competition in non-autonomous Hamiltonian Systems
In this work we use the formalism of chord functions (\emph{i.e.}
characteristic functions) to analytically solve quadratic non-autonomous
Hamiltonians coupled to a reservoir composed by an infinity set of oscillators,
with Gaussian initial state. We analytically obtain a solution for the
characteristic function under dissipation, and therefore for the determinant of
the covariance matrix and the von Neumann entropy, where the latter is the
physical quantity of interest. We study in details two examples that are known
to show dynamical squeezing and instability effects: the inverted harmonic
oscillator and an oscillator with time dependent frequency. We show that it
will appear in both cases a clear competition between instability and
dissipation. If the dissipation is small when compared to the instability, the
squeezing generation is dominant and one can see an increasing in the von
Neumann entropy. When the dissipation is large enough, the dynamical squeezing
generation in one of the quadratures is retained, thence the growth in the von
Neumann entropy is contained
Nonsequential Double Ionization with Polarization-gated Pulses
We investigate laser-induced nonsequential double ionization by a
polarization-gated laser pulse, constructed employing two counter-rotating
circularly polarized few cycle pulses with a time delay . We address the
problem within a classical framework, and mimic the behavior of the
quantum-mechanical electronic wave packet by means of an ensemble of classical
electron trajectories. These trajectories are initially weighted with the
quasi-static tunneling rate, and with suitably chosen distributions for the
momentum components parallel and perpendicular to the laser-field polarization,
in the temporal region for which it is nearly linearly polarized. We show that,
if the time delay is of the order of the pulse length, the
electron-momentum distributions, as functions of the parallel momentum
components, are highly asymmetric and dependent on the carrier-envelope (CE)
phase. As this delay is decreased, this asymmetry gradually vanishes. We
explain this behavior in terms of the available phase space, the quasi-static
tunneling rate and the recollision rate for the first electron, for different
sets of trajectories. Our results show that polarization-gating technique may
provide an efficient way to study the NSDI dynamics in the single-cycle limit,
without employing few-cycle pulses.Comment: 17 pages, 6 figure
Causality and quantum interference in time-delayed laser-induced nonsequential double ionization
We perform a detailed analysis of the importance of causality within the strong-field approximation and the steepest-descent framework for the recollision-excitation with subsequent tunneling ionization (RESI) pathway in laser-induced nonsequential double ionization (NSDI). In this time-delayed pathway, an electron returns to its parent ion and, by recolliding with the core, gives part of its kinetic energy to excite a second electron at a time t′. The second electron then reaches the continuum at a later time t by tunneling ionization. We show that, if t′ and t are complex, the condition that recollision of the first electron occurs before tunnel ionization of the second electron translates into boundary conditions for the steepest-descent contours and thus puts constraints on the saddles to be taken when computing the RESI transition amplitudes. We also show that this generalized causality condition has a dramatic effect on the shapes of the RESI electron momentum distributions for few-cycle laser pulses. Physically, causality determines how the dominant sets of orbits of an electron returning to its parent ion can be combined with the dominant orbits of a second electron tunneling from an excited state. All features encountered are analyzed in terms of such orbits and their quantum interference
Controle genético da reação do feijoeiro comum ao vírus do mosaico dourado.
O objetivo deste trabalho foi obter informações básicas sobre o controle genético da reação do feijoeiro comum ao VMDF que ocorre no Brasil. Foram realizados cinco cruzamentos entre linhagens/cultivares de feijoeiro comum envolvendo sempre um genitor como fonte de tolerância ao VMDF, previamente identificada, e outro, suscetível, como fonte de adaptação, e com características comerciais desejáveis.bitstream/CNPAF/23531/1/bolpesq_15.pd
Finding Out The Neurological Consequences Of Covid-19
t- Introduction: Since the first official case of COVID-19 in China in December 2019, researchers have been trying to uncover the mechanism of action of the severe acute respiratory syndrome Coronavirus 2 (Sars-CoV-2), which attacks several organs in addition to the lungs and causes circulatory changes that can lead to death not only from lung failure but also due to commitment of other organs. Objective: The aim of this study is to find out the neurological consequences of COVID-19. Material and methods: A systematic review of the literature was concretised by mobilizing the descriptors:
"Sars-Cov-2", "coronavirus infections" and "Neurological Consequences". Databases were selected and seven articles were included for analysis. Results and discussion: Although the effects of Sars-CoV-2 on the lung are exemplary and frightening, the long-term effects on the nervous system may be greater and even more overwhelming, as the regeneration of nerve tissue is difficult and can lead to general disability, as the nervous system coordinates the functions of the entire body. All studies show the presence of any kind of injury (mild or severe) to Central Nervous System, but some of them highlight the need for further studies to have great certainty. Conclusion: It can be said that the studies all agree on the possibility of existing neurological sequelae and a majority agree on the need for other studies.info:eu-repo/semantics/publishedVersio
Oral Tolerance: Therapeutic Implications for Autoimmune Diseases
Oral tolerance is classically defined as the suppression of immune responses to antigens (Ag) that have been administered previously by the oral route. Multiple mechanisms of tolerance are induced by oral Ag. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral Ag induces Th2 (IL-4/IL-10) and Th3 (TGF-β) regulatory T cells (Tregs) plus CD4+CD25+ regulatory cells and LAP+T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-β, cholera toxin B subunit (CTB), Flt-3 ligand, anti-CD40 ligand and continuous feeding of Ag. In addition to oral tolerance, nasal tolerance has also been shown to be effective in suppressing inflammatory conditions with the advantage of a lower dose requirement. Oral and nasal tolerance suppress several animal models of autoimmune diseases including experimental allergic encephalomyelitis (EAE), uveitis, thyroiditis, myasthenia, arthritis and diabetes in the nonobese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, colitis and stroke. Oral tolerance has been tested in human autoimmune diseases including MS, arthritis, uveitis and diabetes and in allergy, contact sensitivity to DNCB, nickel allergy. Positive results have been observed in phase II trials and new trials for arthritis, MS and diabetes are underway. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time and Ag-specific mechanism of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy and early therapy
Distinguishing the albedo of exoplanets from stellar activity
Light curves show the flux variation from the target star and its orbiting
planets as a function of time. In addition to the transit features created by
the planets, the flux also includes the reflected light component of each
planet, which depends on the planetary albedo. This signal is typically
referred to as phase curve and could be easily identified if there were no
additional noise. As well as instrumental noise, stellar activity, such as
spots, can create a modulation in the data, which may be very difficult to
distinguish from the planetary signal. We analyze the limitations imposed by
the stellar activity on the detection of the planetary albedo, considering the
limitations imposed by the predicted level of instrumental noise and the short
duration of the observations planned in the context of the CHEOPS mission. As
initial condition, we have assumed that each star is characterized by just one
orbiting planet. We built mock light curves that included a realistic stellar
activity pattern, the reflected light component of the planet and an
instrumental noise level, which we have chosen to be at the same level as
predicted for CHEOPS. We then fit these light curves to try to recover the
reflected light component, assuming the activity patterns can be modeled with a
Gaussian process.We estimate that at least one full stellar rotation is
necessary to obtain a reliable detection of the planetary albedo. This result
is independent of the level of noise, but it depends on the limitation of the
Gaussian process to describe the stellar activity when the light curve
time-span is shorter than the stellar rotation. Finally, in presence of typical
CHEOPS gaps in the simulations, we confirm that it is still possible to obtain
a reliable albedo.Comment: Accepted for publication in A&A, 14 pages, 12 figure
Interference effects in above-threshold ionization from diatomic molecules: determining the internuclear separation
We calculate angle-resolved above-threshold ionization spectra for diatomic
molecules in linearly polarized laser fields, employing the strong-field
approximation. The interference structure resulting from the individual
contributions of the different scattering scenarios is discussed in detail,
with respect to the dependence on the internuclear distance and molecular
orientation. We show that, in general, the contributions from the processes in
which the electron is freed at one center and rescatters off the other obscure
the interference maxima and minima obtained from single-center processes.
However, around the boundary of the energy regions for which rescattering has a
classical counterpart, such processes play a negligible role and very clear
interference patterns are observed. In such energy regions, one is able to
infer the internuclear distance from the energy difference between adjacent
interference minima.Comment: 10 pages, 8 figures; discussions slightly modified and an additional
figure inserted for clarit
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