3,966 research outputs found
Host choice and host leaving in Rhopalosiphum padi (Hemiptera: Aphididae) emigrants and repellency of aphid colonies on the winter host
Host choice and winter-host leaving in emigrants of bird cherry–oat aphid,
Rhopalosiphum padi (Linnaeus), were investigated in the laboratory. In settling
choice tests, emigrants collected from the winter host, Prunus padus, preferred this
plant over a summer host, oats. Emigrants which had left P. padus for up to 24 h
did not express a preference as a group, and those which had left for 24–48 h
preferred oats. Eighty seven percent of emigrants caged as fourth-instar nymphs
on P. padus leaves abandoned the host by the second day of adult life, and
apparently did not subsequently return to the leaf. In an olfactometer, P. padus
leaves which had supported spring generations of R. padi were repellent to
emigrants. Volatiles were entrained from uninfested and R. padi-infested P. padus
using cut twigs in the laboratory as well as intact twigs on a tree in the field.
Entrainment extracts from uninfested P. padus had no effect on emigrants in the
olfactometer, whereas those from twigs infested with nymphal emigrants were
repellent. The study indicates that in R. padi, host-alternation is driven by
behavioural changes which occur in individuals as well as between morphs
Field Tuning the G-Factor in InAs Nanowire Double Quantum Dots
We study the effects of magnetic and electric fields on the g-factors of
spins confined in a two-electron InAs nanowire double quantum dot. Spin
sensitive measurements are performed by monitoring the leakage current in the
Pauli blockade regime. Rotations of single spins are driven using
electric-dipole spin resonance. The g-factors are extracted from the spin
resonance condition as a function of the magnetic field direction, allowing
determination of the full g-tensor. Electric and magnetic field tuning can be
used to maximize the g-factor difference and in some cases altogether quench
the EDSR response, allowing selective single spin control.Comment: Related papers at http://pettagroup.princeton.ed
Random matrix model for QCD_3 staggered fermions
We show that the lowest part of the eigenvalue density of the staggered
fermion operator in lattice QCD_3 at small lattice coupling constant beta has
exactly the same shape as in QCD_4. This observation is quite surprising, since
universal properties of the QCD_3 Dirac operator are expected to be described
by a non-chiral matrix model. We show that this effect is related to the
specific nature of the staggered fermion discretization and that the eigenvalue
density evolves towards the non-chiral random matrix prediction when beta is
increased and the continuum limit is approached. We propose a two-matrix model
with one free parameter which interpolates between the two limits and very well
mimics the pattern of evolution with beta of the eigenvalue density of the
staggered fermion operator in QCD_3.Comment: 8 pages 4 figure
Phase metrology with multi-cycle two-colour pulses
Strong-field phenomena driven by an intense infrared (IR) laser depend on
during what part of the field cycle they are initiated. By changing the
sub-cycle character of the laser electric field it is possible to control such
phenomena. For long pulses, sub-cycle shaping of the field can be done by
adding a relatively weak, second harmonic of the driving field to the pulse.
Through constructive and destructive interference, the combination of strong
and weak fields can be used to change the probability of a strong-field process
being initiated at any given part of the cycle. In order to control sub-cycle
phenomena with optimal accuracy, it is necessary to know the phase difference
of the strong and the weak fields precisely. If the weaker field is an even
harmonic of the driving field, electrons ionized by the field will be
asymmetrically distributed between the positive and negative directions of the
combined fields. Information about the asymmetry can yield information about
the phase difference. A technique to measure asymmetry for few-cycle pulses,
called Stereo-ATI (Above Threshold Ionization), has been developed by [Paulus G
G, et al 2003 Phys. Rev. Lett. 91]. This paper outlines an extension of this
method to measure the phase difference between a strong IR and its second
harmonic
Radio frequency charge sensing in InAs nanowire double quantum dots
We demonstrate charge sensing of an InAs nanowire double quantum dot (DQD)
coupled to a radio frequency (rf) circuit. We measure the rf signal reflected
by the resonator using homodyne detection. Clear single dot and DQD behavior
are observed in the resonator response. rf-reflectometry allows measurements of
the DQD charge stability diagram in the few-electron regime even when the dc
current through the device is too small to be measured. For a signal-to-noise
ratio of one, we estimate a minimum charge detection time of 350 microseconds
at interdot charge transitions and 9 microseconds for charge transitions with
the leads.Comment: Related papers at http://pettagroup.princeton.ed
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