4,584 research outputs found
Developmental and physiological studies of bracken (Pteridium aquilinum)
The application of 2,4-D to the frond of the bracken sporeling induces an abundant proliferation of roots at the apices of the rhizome and a temporary inhibition of rhizome development. The failure of these effects to be produced when a segment of the treated frond had been killed indicated that the basipetal transport of the herbicide occurs in living tissues. The number of roots induced and the inhibition of rhizome development increases with the dosage applied while the elongation of the roots is correspondingly depressed. There is evidence that the direction of translocation within the rhizome is dependent upon the position of the treated frond, movement being greater into that branch arising on the same side of the stem as that on which the treated frond is inserted. This relationship is attributed to the nature of the vascular connections. The induction of large numbers of root primordia at the rhizome apices was found to be the most characteristic of the histological effects. It has also been shown that the application of 2,4-D to fully expanded fronds of mature bracken produces injurious effects at the apices of the rhizomes. The effects were similar to those induced by this treatment in the young sporeling. Autoradiograms from sporeling fronds treated with 2,4-D containing radioactive carbon (C14) showed that the direction of translocation is largely determined by the stage of development of the frond and provided good evidence that the herbicide is translocated in association with food materials. Employing the same technique in a field experiment it was found that the amount of the tracer which moved into the rhizome was considerably greater from parts of the frond which were still immature. It is suggested, as a possible explanation of this result, that the penetration of the herbicide may be restricted by changes associated with the maturation of the frond
A Laser System for the Spectroscopy of Highly-Charged Bismuth Ions
We present and characterize a laser system for the spectroscopy on
highly-charged ^209Bi^82+ ions at a wavelength of 243.87 nm. For absolute
frequency stabilization, the laser system is locked to a near-infra-red laser
stabilized to a rubidium transition line using a transfer cavity based locking
scheme. Tuning of the output frequency with high precision is achieved via a
tunable rf offset lock. A sample-and-hold technique gives an extended tuning
range of several THz in the UV. This scheme is universally applicable to the
stabilization of laser systems at wavelengths not directly accessible to atomic
or molecular resonances. We determine the frequency accuracy of the laser
system using Doppler-free absorption spectroscopy of Te_2 vapour at 488 nm.
Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty
of \sigma_{244nm} = 6.14 MHz (one standard deviation) over six days of
operation.Comment: Contribution to the special issue on "Trapped Ions" in "Applied
Physics B
Electron mobility in surface- and buried- channel flatband In<sub>0.53</sub>Ga<sub>0.47</sub>As MOSFETs with ALD Al<sub>2</sub>O<sub>3</sub> gate dielectric.
In this paper, we investigate the scaling potential of flatband III-V MOSFETs by comparing the mobility of surface and buried In<sub>0.53</sub>Ga<sub>0.47</sub>As channel devices employing an Atomic Layer Deposited (ALD) Al<sub>2</sub>O<sub>3</sub> gate dielectric and a delta-doped InGaAs/InAlAs/InP heterostructure.
Peak electron mobilities of 4300 cm<sup>2</sup>/V·s and 6600 cm<sup>2</sup>/V·s at a carrier density of 3×1012 cm<sup>-2</sup> for the surface and buried channel structures respectively were determined. In contrast to similarly scaled inversion-channel devices, we find that mobility in surface channel flatband structures does not drop rapidly with electron density, but rather high mobility is maintained up to carrier concentrations around 4x10<sup>12</sup> cm<sup>-2</sup> before slowly dropping to around 2000 cm<sup>2</sup>/V·s at 1x10M<sup>13</sup> cm<sup>-2</sup>. We believe these to be world leading metrics for this material system and an important development in informing the III-V MOSFET device architecture selection process for future low power, highly scaled CM
Lattice and magnetic instabilities in CaFe2As2: A single crystal neutron diffraction study
Neutron diffraction measurements of a high quality single crystal of CaFe2As2
are reported. A sharp transition was observed between the high temperature
tetragonal and low temperature orthorhombic structures at TS = 172.5K (on
cooling) and 173.5K (on warming). Coincident with the structural transition we
observe a rapid, but continuous, ordering of the Fe moments, in a commensurate
antiferromagnetic structure is observed, with a saturated moment of
0.80(5)muB/Fe directed along the orthorhombic a-axis. The hysteresis of the
structural transition is 1K between cooling and warming and is consistent with
previous thermodynamic, transport and single crystal x-ray studies. The
temperature onset of magnetic ordering shifts rigidly with the structural
transition providing the clearest evidence to date of the coupling between the
structural and magnetic transitions in this material and the broader class of
iron arsenides.Comment: submitted to PR
Identifying Old Tidal Dwarf Irregulars
We examine the observational consequences of the two possible origins for
irregular galaxies: formation from collapse of a primordial cloud of gas early
in the age of the Universe, and formation from tidal tails in an interaction
that could have occured any time in the history of the Universe. Because the
formation from tidal tails could have occurred a long time ago, proximity to
larger galaxies is not sufficient to distinguish tidal dwarfs from traditional
dwarfs. We consider the effects of little or no dark matter on rotation speeds
and the Tully-Fisher relationship, the metallicity-luminosity relationship,
structure, and stellar populations. From these selection criteria, we identify
a small list of dwarf irregular galaxies that are candidates for having formed
as tidal dwarfs.Comment: ApJ, to appear September 20, 200
Jahn-Teller versus quantum effects in the spin-orbital material LuVO3
We report on combined neutron and resonant x-ray scattering results,
identifying the nature of the spin-orbital ground state and magnetic
excitations in LuVO3 as driven by the orbital parameter. In particular, we
distinguish between models based on orbital Peierls dimerization, taken as a
signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor
of the latter. In order to solve this long-standing puzzle, polarized neutron
beams were employed as a prerequisite in order to solve details of the magnetic
structure, which allowed quantitative intensity-analysis of extended magnetic
excitation data sets. The results of this detailed study enabled us to draw
definite conclusions about classical vs quantum behavior of orbitals in this
system and to discard the previous claims about quantum effects dominating the
orbital physics of LuVO3 and similar systems.Comment: Phys. Rev. B 91, 161104(R) (2015
Microscopic description of the beta delayed deuteron emission from \bbox{^6}He
The beta delayed deuteron emission from He is studied in a dynamical
microscopic cluster model. This model gives a reasonably good description for
all the subsystems of He and Li in a coherent way, without any free
parameter. The beta decay transition probability to the Li ground state is
underestimated by a few percents. The theoretical beta delayed deuteron
spectrum is close to experiment but it is also underestimated by about a factor
1.7. We argue that, in spite of their different magnitudes, both
underestimations might have a common origin. The model confirms that the
neutron halo part of the He wave function plays a crucial role in quenching
the beta decay toward the + d channel.Comment: LATEX with REVTEX, Submitted to Phys. Rev. C, 11 pages, 3 figures
(not included) are available upon request. ATOMKI-93/
Optimization of the reverse transcriptase polymerase chain reaction for the detection of circulating prostate cells
The reverse transcriptase polymerase chain reaction (RT-PCR) is a sensitive technique that can detect prostate-specific messenger RNA in circulating blood. Many authors have studied the potential of RT-PCR as a staging technique in prostate cancer (PC). Clinical sensitivity and in some cases specificity has been disappointing. Few authors have been able to correlate RT-PCR result with patient stage. We have compared the results of using two different RT-PCR protocols with different sensitivities on blood samples from prostate cancer patients. An 80-amplification-cycle nested primer RT-PCR assay had a detection limit of 10 prostate cells and a 50-cycle RT-PCR could detect 20 cells in 5 ml blood. The 80-cycle assay detected prostate mRNA in four of 10 female samples, whereas the 50-cycle assay detected it in none. There was little difference in the assays’ ability to detect prostate mRNA in advanced PC patients. The 50-cycle assay could differentiate between hormone-escaped, stable hormone-treated and untreated localized PC patients, whereas the 80-cycle assay could not. Each blood sample must be assayed several times with RT-PCR to avoid false-negative results and, if this is done, assay specificity can be increased with little effect on clinical sensitivity. © 2000 Cancer Research Campaig
Radio Supernova 1987A at 843 MHz
We report the flux densities of the evolving radio source SN1987A at 843 MHz
measured from observations made with the Molonglo Observatory Synthesis
Telescope between 1994 September and 2000 May. The radio light curve shows that
the rate of increase of the flux density jumped markedly around days 2800-3000
(i.e. in the first half of 1995), and that since then the radio evolution has
been remarkably well fitted by a simple linear increase of (62.7 +- 0.5)
microJansky/day. We discuss in detail the relationship between the radio light
curve and the recent brightening of the system at optical wavelengths.Comment: To be published in the Astrophysical Journal, 11 pages, 4 postscript
figure
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