41,258 research outputs found
Distributed feedback lasers
A ridge waveguide distributed feedback laser was developed in InGaAsP. These devices have demonstrated CW output powers over 7 mW with threshold currents as low as 60 mA at 25 C. Measurements of the frequency response of these devices show a 3 dB bandwidth of about 2 GHz, which may be limited by the mount. The best devices have a single mode spectra over the entire temperature range tested with a side mode suppression of about 20 dB in both CW and pulsed modes. The design of this device, including detailed modeling of the ridge guide structure, effective index calculations, and a discussion of the grating configuration are presented. Also, the fabrication of the devices is presented in some detail, especially the fabrication of and subsequent growth over the grating. In addition, a high frequency fiber pigtailed package was designed and tested, which is a suitable prototype for a commercial package
Work probability distribution in single molecule experiments
We derive and solve a differential equation satisfied by the probability
distribution of the work done on a single biomolecule in a mechanical unzipping
experiment. The unzipping is described as a thermally activated escape process
in an energy landscape. The Jarzynski equality is recovered as an identity,
independent of the pulling protocol. This approach allows one to evaluate
easily, by numerical integration, the work distribution, once a few parameters
of the energy landscape are known.Comment: To appear on EP
Interactions between unidirectional quantized vortex rings
We have used the vortex filament method to numerically investigate the
interactions between pairs of quantized vortex rings that are initially
traveling in the same direction but with their axes offset by a variable impact
parameter. The interaction of two circular rings of comparable radii produce
outcomes that can be categorized into four regimes, dependent only on the
impact parameter; the two rings can either miss each other on the inside or
outside, or they can reconnect leading to final states consisting of either one
or two deformed rings. The fraction of of energy went into ring deformations
and the transverse component of velocity of the rings are analyzed for each
regime. We find that rings of very similar radius only reconnect for a very
narrow range of the impact parameter, much smaller than would be expected from
geometrical cross-section alone. In contrast, when the radii of the rings are
very different, the range of impact parameters producing a reconnection is
close to the geometrical value. A second type of interaction considered is the
collision of circular rings with a highly deformed ring. This type of
interaction appears to be a productive mechanism for creating small vortex
rings. The simulations are discussed in the context of experiments on colliding
vortex rings and quantum turbulence in superfluid helium in the zero
temperature limit
Recommended from our members
Replication enhancer elements within the open reading frame of tick-borne encephalitis virus and their evolution within the Flavivirus genus
We provide experimental evidence of a replication enhancer element (REE) within the capsid gene of tick-borne encephalitis virus (TBEV, genus Flavivirus). Thermodynamic and phylogenetic analyses predicted that the REE folds as a long stable stem–loop (designated SL6), conserved among all tick-borne flaviviruses (TBFV). Homologous sequences and potential base pairing were found in the corresponding regions of mosquito-borne flaviviruses, but not in more genetically distant flaviviruses. To investigate the role
of SL6, nucleotide substitutions were introduced which changed a conserved hexanucleotide motif, the conformation of the terminal loop and the base-paired dsRNA stacking. Substitutions were made within a TBEV reverse genetic system and recovered mutants were compared for plaque
morphology, single-step replication kinetics and cytopathic effect. The greatest phenotypic changes were observed in mutants with a destabilized stem. Point mutations in the conserved hexanucleotide motif of the terminal loop caused
moderate virus attenuation. However, all mutants
eventually reached the titre of wild-type virus late post-infection. Thus, although not essential for growth in tissue culture, the SL6 REE acts to up-regulate virus replication. We hypothesize that this modulatory role may be important for TBEV survival in nature, where the virus circulates by non-viraemic transmission between infected and
non-infected ticks, during co-feeding on local rodents
Academic rejection: The coping strategies of women
This paper offers insights into the coping strategies employed by women researchers when handling academic rejection. Female researchers identify four main coping strategies for handling the rejection of an academic paper and the failure of a funding application. The study identified common coping strategies implemented by academic women, and determines whether these strategies are consistent regardless of the type of rejection being dealt with. The research found conflicting responses from the women between their tips or suggestions to others on how to best handle rejection, and the actual coping strategies employed
Understanding the effect resonant magnetic perturbations have on ELMs
All current estimations of the energy released by type I ELMs indicate that,
in order to ensure an adequate lifetime of the divertor targets on ITER, a
mechanism is required to decrease the amount of energy released by an ELM, or
to eliminate ELMs altogether. One such amelioration mechanism relies on
perturbing the magnetic field in the edge plasma region, either leading to more
frequent, smaller ELMs (ELM mitigation) or ELM suppression. This technique of
Resonant Magnetic Perturbations (RMPs) has been employed to suppress type I
ELMs at high collisionality/density on DIII-D, ASDEX Upgrade, KSTAR and JET and
at low collisionality on DIII-D. At ITER-like collisionality the RMPs enhance
the transport of particles or energy and keep the edge pressure gradient below
the 2D linear ideal MHD critical value that would trigger an ELM, whereas at
high collisionality/density the type I ELMs are replaced by small type II ELMs.
Although ELM suppression only occurs within limitied operational ranges, ELM
mitigation is much more easily achieved. The exact parameters that determine
the onset of ELM suppression are unknown but in all cases the magnetic
perturbations produce 3D distortions to the plasma and enhanced particle
transport. The incorporation of these 3D effects in codes will be essential in
order to make quantitative predictions for future devices.Comment: 32 pages, 9 figure
Higgs Mechanism in String Theory
In first-quantized string theory, spacetime symmetries are described by inner
automorphisms of the underlying conformal field theory. In this paper we use
this approach to illustrate the Higgs effect in string theory. We consider
string propagation on M^{24,1} \times S^1, where the circle has radius R, and
study SU(2) symmetry breaking as R moves away from its critical value. We find
a gauge-covariant equation of motion for the broken-symmetry gauge bosons and
the would-be Goldstone bosons. We show that the Goldstone bosons can be
eliminated by an appropriate gauge transformation. In this unitary gauge, the
Goldstone bosons become the longitudinal components of massive gauge bosons.Comment: 12 pages, Te
The Effect of Weak Interactions on the Ultra-Relativistic Bose-Einstein Condensation Temperature
We calculate the ultra-relativistic Bose-Einstein condensation temperature of
a complex scalar field with weak lambda Phi^4 interaction. We show that at high
temperature and finite density we can use dimensional reduction to produce an
effective three-dimensional theory which then requires non-perturbative
analysis. For simplicity and ease of implementation we illustrate this process
with the linear delta expansion.Comment: Latex2e, 12 pages, three eps figures, replacement with additional
discussion and extra figur
Inverse meson mass ordering in color-flavor-locking phase of high density QCD: erratum
We correct a mistake in the calculation of meson masses at large baryon
chemical potential made in hep-ph/9910491v2Comment: 2 pages, 1 figure, erratum to hep-ph/9910491v
- …