6 research outputs found
Multimode dynamics in a short-pulse THz free electron laser
The interaction of waveguide modes and consequences on laser operation are studied numerically in a THz free electron laser (FEL) driven by short electron bunches. The considered FEL cavity configuration is represented by a parallel-plate waveguide extending over the complete distance between cylindrical cavity mirrors with energy out-coupling through a rectangular slit in one of the mirrors. We describe the multimode FEL cavity desynchronization dynamics and predict strong enhancement in FEL power at special cavity configurations, when modes are degenerate. Furthermore, we predict that simultaneous excitation of several waveguide modes can occur but do not negatively influence the lasing process
Nonlinear Terahertz transmission spectroscopy on Ga-doped germanium in high magnetic fields
2D “Soap”-Assembly of Nanoparticles via Colloid-Induced Condensation of Mixed Langmuir Monolayers of Fatty Surfactants
We describe a new type of colloidal 2D gels formed in mixed Langmuir
monolayers of stearic acid and octadecylamine on a surface of gold
hydrosol. The adsorption of gold nanoparticles on the mixed monolayer
led to an increase of interactions between oppositely charged surfactants
giving a “soap” of mixed fatty salt. The observed effect
is equivalent to a virtual “cooling” of floating monolayer,
which undergoes rapid condensation on a surface of aqueous colloid.
The consequent shrinking and rearrangement of the monolayer resulted
in aggregation of nanoparticles into colloidal 2D “soap”-gels,
which represented arrested colloidal phases within nonadsorbing organic
medium. When sequentially deposited onto solids by Langmuir–Blodgett
technique, the 2D “soap”-gels separated into organic
and colloidal phases and gave dendrite-like bilateral organic crystallites
coated with gold nanoparticles. The reported colloidal “soap”-assembly
can offer a new opportunity to design 2D colloidal systems of widely
variable chemistry and structures
The Significance of the Amorphous Potential Energy Landscape for Dictating Glassy Dynamics and Driving Solid-State Crystallisation
The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials
can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and
even large biological systems. The glass-transition temperature, Tg, can be readily detected by
a diverse set of techniques, but given that these measurement modalities probe vastly different
processes, there has been significant debate regarding the question of why Tg can be detected
across all of them. Here we show clear experimental and computational evidence in support of
a theory that proposes that the shape and structure of the potential-energy surface (PES) is the
fundamental factor underlying the glass-transition processes, regardless of the frequency that experimental methods probe. Whilst this has been proposed previously, we demonstrate, using ab
initio molecular-dynamics (AIMD) simulations, that it is of critical importance to carefully consider
the complete PES – both the intra-molecular and inter-molecular features – in order to fully un-
derstand the entire range of atomic-dynamical processes in disordered solids. Finally, we show
that it is possible to utilise this dependence to directly manipulate and harness amorphous dynamics in order to control the behaviour of such solids by using high-powered terahertz pulses to
induce crystallisation and preferential crystal-polymorph growth in glasses. Combined, these findings provide direct evidence that the PES landscape, and the corresponding energy barriers, are
the ultimate controlling feature behind the atomic and molecular dynamics of disordered solids,
regardless of the frequency at which they occur.
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Current methods for detecting ethylene in plants.
In view of ethylene's critical developmental and physiological roles the gaseous hormone remains an active research topic for plant biologists. Progress has been made to understand the ethylene biosynthesis pathway and the mechanisms of perception and action. Still numerous questions need to be answered and findings to be validated. Monitoring gas production will very often complete the picture of any ethylene research topic. Therefore the search for suitable ethylene measuring methods for various plant samples either in the field, greenhouses, laboratories or storage facilities is strongly motivated.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: re.jinfo:eu-repo/semantics/publishe