3,518 research outputs found
Transtheoretical principles and processes for quitting smoking: A 24-month comparison of a representative sample of quitters, relapsers, and non-quitters
This longitudinal study compared 14 principles and processes of change applied by successful quitters, relapsers and non-quitters over 24 months in a representative sample of 4144 smokers in intervention and control groups. The successful quitters showed a decrease in the use of experiential processes (cognitive, affective and effective) and an increase in behavioral processes (e.g., counter-conditioning and stimulus control). The non-quitters showed little change in their use of almost all of the processes. The relapsers\u27 use of the processes tended to initially parallel the successful quitters, but over time, their use ended up between the quitters and the non-quitters. In general, the relapsers ended up working harder but not smarter than the successful quitters. The pattern of use of change processes in the treatment and control groups were remarkably similar, suggesting common pathways to change
Fabrication and Characterization of Topological Insulator BiSe Nanocrystals
In the recently discovered class of materials known as topological
insulators, the presence of strong spin-orbit coupling causes certain
topological invariants in the bulk to differ from their values in vacuum. The
sudden change of invariants at the interface results in metallic, time reversal
invariant surface states whose properties are useful for applications in
spintronics and quantum computation. However, a key challenge is to fabricate
these materials on the nanoscale appropriate for devices and probing the
surface. To this end we have produced 2 nm thick nanocrystals of the
topological insulator BiSe via mechanical exfoliation. For crystals
thinner than 10 nm we observe the emergence of an additional mode in the Raman
spectrum. The emergent mode intensity together with the other results presented
here provide a recipe for production and thickness characterization of
BiSe nanocrystals.Comment: 4 pages, 3 figures (accepted for publication in Applied Physics
Letters
Highly efficient double ionization of mixed alkali dimers by intermolecular Coulombic decay
As opposed to purely molecular systems where electron dynamics proceed only
through intramolecular processes, weakly bound complexes such as He droplets
offer an environment where local excitations can interact with neighbouring
embedded molecules leading to new intermolecular relaxation mechanisms. Here,
we report on a new decay mechanism leading to the double ionization of alkali
dimers attached to He droplets by intermolecular energy transfer. From the
electron spectra, the process is similar to the well-known shake-off mechanism
observed in double Auger decay and single-photon double ionization, however, in
this case, the process is dominant, occurring with efficiencies equal to, or
greater than, single ionization by energy transfer. Although an alkali dimer
attached to a He droplet is a model case, the decay mechanism is relevant for
any system where the excitation energy of one constituent exceeds the double
ionization potential of another neighbouring molecule. The process is, in
particular, relevant for biological systems, where radicals and slow electrons
are known to cause radiation damageComment: accepted as Nature Physic
Three-body Dynamics in Single Ionization of Atomic Hydrogen by 75 KeV Proton Impact
Doubly differential cross sections for single ionization of atomic hydrogen by 75 keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. This pure three-body collision system represents a fundamental test case for the study of the reaction dynamics in few-body systems. A comparison between theory and experiment reveals that three-body dynamics is important at all scattering angles and that an accurate description of the role of the projectile-target-nucleus interaction remains a major challenge to theory
Collective Autoionization in Multiply-Excited Systems: A novel ionization process observed in Helium Nanodroplets
Free electron lasers (FELs) offer the unprecedented capability to study
reaction dynamics and image the structure of complex systems. When multiple
photons are absorbed in complex systems, a plasma-like state is formed where
many atoms are ionized on a femtosecond timescale. If multiphoton absorption is
resonantly-enhanced, the system becomes electronically-excited prior to plasma
formation, with subsequent decay paths which have been scarcely investigated to
date. Here, we show using helium nanodroplets as an example that these systems
can decay by a new type of process, named collective autoionization. In
addition, we show that this process is surprisingly efficient, leading to ion
abundances much greater than that of direct single-photon ionization. This
novel collective ionization process is expected to be important in many other
complex systems, e.g. macromolecules and nanoparticles, exposed to high
intensity radiation fields
Inelastic scattering of photoelectrons from He nanodroplets
We present a detailed study of inelastic energy-loss collisions of
photoelectrons emitted from He nanodroplets by tunable extreme ultraviolet
(XUV) radiation. Using coincidence imaging detection of electrons and ions, we
probe the lowest He droplet excited states up to the electron impact ionization
threshold. We find significant signal contributions from photoelectrons emitted
from free He atoms accompanying the He nanodroplet beam. Furthermore, signal
contributions from photoionization and electron impact excitation/ionization
occurring in pairs of nearest-neighbor atoms in the He droplets are detected.
This work highlights the importance of inelastic electron scattering in the
interaction of nanoparticles with XUV radiation
Real-time dynamics of the formation of hydrated electrons upon irradiation of water clusters with extreme ultraviolet light
Free electrons in a polar liquid can form a bound state via interaction with the molecular environment. This so-called hydrated electron state in water is of fundamental importance e.g.~in cellular biology or radiation chemistry. Hydrated electrons are highly reactive radicals that can either directly interact with DNA or enzymes, or form highly excited hydrogen (H∗) after being captured by protons. Here, we investigate the formation of the hydrated electron in real-time employing XUV femtosecond pulses from a free electron laser, in this way observing the initial steps of the hydration process. Using time-resolved photoelectron spectroscopy we find formation timescales in the low picosecond range and resolve the prominent dynamics of forming excited hydrogen states
Two-Stage Rotational Disordering of a Molecular Crystal Surface: C60
We propose a two-stage mechanism for the rotational surface disordering phase
transition of a molecular crystal, as realized in C fullerite. Our
study, based on Monte Carlo simulations, uncovers the existence of a new
intermediate regime, between a low temperature ordered state,
and a high temperature disordered phase. In the intermediate
regime there is partial disorder, strongest for a subset of particularly
frustrated surface molecules. These concepts and calculations provide a
coherent understanding of experimental observations, with possible extension to
other molecular crystal surfaces.Comment: 4 pages, 2 figure
Interference Effects Due to Projectile Target Nucleus Scattering in Single Ionization of H₂ by 75-keV Proton Impact
Doubly differential cross sections (DDCSs) for single ionization of molecular hydrogen by 75-keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. Interference structures are observed in the scattering angular dependence of the DDCSs, which disappear, however, at electron speeds near the projectile speed. The comparison to our calculations shows that the projectile-target nucleus interaction plays a central role. Furthermore, our data suggest that for a given scattering angle, ionization favors well-defined molecular orientations
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