645 research outputs found
A method to detect baseline emission and plant damage induced volatile emission in a greenhouse
The objective of this research was to ascertain if 1) baseline emission and 2) damage induced emission of volatile plant substances could be detected under greenhouse conditions. A laboratory method was validated for analysing the air in a semi-closed greenhouse with 44 m2 floor area. This greenhouse, with a volume of 270 m3, was climate controlled and light was supplied with assimilation lamps. Sixty tomato plants (Lycopersicon esculentum Mill cv. Moneymaker) were grown in this greenhouse. These plants were artificially damaged on a weekly interval by stroking the stems. Continuous flow pumps were used to purge the air surrounding the plants through tubes containing an adsorbent. This sampling step was performed before and directly after damage of the plants. After sampling, the tubes were transferred to the lab for analysis. The analysis of volatile compounds was performed using a high-throughput gas chromatography-mass spectrometry system. The method enabled the detection of baseline level emission and the emission of volatiles released after artificially damaging the tomato plants during a 6 weeks growing period. Most dominant compounds for baseline emission were the monoterpenes ß-phellandrene, 2-carene, limonene, ¿-phellandrene and ¿-pinene. Directly after damage, these compounds showed an increase of up to 100 times compared to baseline level emission. With these results, we prove that it is possible to detect baseline- and plant damage induced volatile emission in a greenhouse. This area of research is promising but more research needs to be done to determine whether it is possible to detect plant damage due to pests and pathogens using volatile sensing
BokSmart: Safe and effective techniques in rugby union
As with any contact sport, rugby union has a high risk of injury. The majority of injuries result from contact phases of play such as the tackle, taking the ball into contact, the scrum, the lineout and the ruck and maul. Many techniques associated with a reduced risk of injury can be taught. The need for coaches to emphasise correct technique is extremely important and one of the few possible modes to reduce injuries, particularly non-fatal catastrophic injuries to the head, neck, brain and spine. This paper provides evidence of safe techniques during the contact phases of the game (tackling, taking the ball into contact, scrum setting and engagement, lineouts as well as rucks and mauls). Examples are also given to show that safe techniques often are the most effective techniques from a performance perspective
Dissociation and ionization of small molecules steered by external noise
We show that ionization and dissociation can be influenced separately in a
molecule with appropriate external noise. Specifically we investigate the
hydrogen molecular ion under a stochastic force quantum mechanically beyond the
Born-Oppenheimer approximation. We find that up to 30% of dissociation without
ionization can be achieved by suitably tuning the forcing parameters.Comment: 13 pages, 6 figure
Dissociation spectrum of H from a short, intense infrared laser pulse: vibration structure and focal volume effects
The dissociation spectrum of the hydrogen molecular ion by short intense
pulses of infrared light is calculated. The time-dependent Schr\"odinger
equation is discretized and integrated in position and momentum space. For
few-cycle pulses one can resolve vibrational structure that commonly arises in
the experimental preparation of the molecular ion from the neutral molecule. We
calculate the corresponding energy spectrum and analyze the dependence on the
pulse time-delay, pulse length, and intensity of the laser for nm. We conclude that the proton spectrum is a both a sensitive probe of the
vibrational dynamics and the laser pulse. Finally we compare our results with
recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire
laser (nm). Integrating over the laser focal volume, for the
intensity W cm, we find our results are in
excellent agreement with these experiments.Comment: 17 pages, 8 figures, preprin
Semiclassical ionization dynamics of the hydrogen molecular ion in an electric field of arbitrary orientation
Quasi-static models of barrier suppression have played a major role in our
understanding of the ionization of atoms and molecules in strong laser fields.
Despite their success, in the case of diatomic molecules these studies have so
far been restricted to fields aligned with the molecular axis. In this paper we
investigate the locations and heights of the potential barriers in the hydrogen
molecular ion in an electric field of arbitrary orientation. We find that the
barriers undergo bifurcations as the external field strength and direction are
varied. This phenomenon represents an unexpected level of intricacy even on
this most elementary level of the dynamics. We describe the dynamics of
tunnelling ionization through the barriers semiclassically and use our results
to shed new light on the success of a recent theory of molecular tunnelling
ionization as well as earlier theories that restrict the electric field to be
aligned with the molecular axis
Enhanced ionization in small rare gas clusters
A detailed theoretical investigation of rare gas atom clusters under intense
short laser pulses reveals that the mechanism of energy absorption is akin to
{\it enhanced ionization} first discovered for diatomic molecules. The
phenomenon is robust under changes of the atomic element (neon, argon, krypton,
xenon), the number of atoms in the cluster (16 to 30 atoms have been studied)
and the fluency of the laser pulse. In contrast to molecules it does not
dissappear for circular polarization. We develop an analytical model relating
the pulse length for maximum ionization to characteristic parameters of the
cluster
The propensity of molecules to spatially align in intense light fields
The propensity of molecules to spatially align along the polarization vector
of intense, pulsed light fields is related to readily-accessible parameters
(molecular polarizabilities, moment of inertia, peak intensity of the light and
its pulse duration). Predictions can now be made of which molecules can be
spatially aligned, and under what circumstances, upon irradiation by intense
light. Accounting for both enhanced ionization and hyperpolarizability, it is
shown that {\it all} molecules can be aligned, even those with the smallest
static polarizability, when subjected to the shortest available laser pulses
(of sufficient intensity).Comment: 8 pages, 4 figures, to be submitted to PR
- …