| 1. |
- Block, K, et al.
(author)
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Characterization of a minichromosome derived from the transposing element TE1 in Drosophila melanogaster
- 1991
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In: Hereditas. - : Wiley-Blackwell Publishing, Inc.. - 0018-0661. ; , s. 82-83
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Conference paper (peer-reviewed)abstract
- The transposing element TEI contains the structural genes white and roughest from the Drosophilr X-chromosome. These genes are flanked by FB-elements, which are responsible for the mobility. At one occasion the TE, probably together with an adjacent segment in chromosome 2. has formed a minichromosome. This chromosome contains both the structural genes, the FB-elements,some centromeric and/or telomeric heterochromatin. It probably has a centromere as well, as it is transferred to the offspring at a high rate. From this minichromosome a smaller one has originated, probably through the loss of the region from chromosome 2 and some heterochromatin. This smaller minichromosome has been characterized in the following way: 1. Size determination hy pulsed field gel electrophoresis. -The chromosome turned out to be little more than one megabase. 2. y-irradiation of DNA from the minichromosome. ~ The aim of this experiment is to find out if the chromosome is circular or linear. A radiation dose which causes one break within a circle ought to accumulate DNA of the same size as the minichromosome. In this case no accumulation occurred and thus the chromosome is probably linear. 3. Cloning of sequences from the minichromosome. ~ A low melting agarose gel was run and a fragment was cut out from a region which contained DNA fragments of the same size as the minichromosome. The DNA was cut simultaneously by EcoR I and Pst I and ligated into the vector pBS containing T7 and T3 primers. The ligated DNA was amplified by the PCR method, which rendered several fragments of varying size. These fragments were ligated into the vector pCR1000TM. Positive clones are being analysed at present. With these clones we intend to construct a map of the minichromosome.
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| 2. |
- Rothwell, P.L., et al.
(author)
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Acceleration and Stochastic Heating of Ions Drifting Through an Auroral Arc
- 1992
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 97, s. 19333-19339
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Journal article (peer-reviewed)abstract
- We find that ions E x B drifting through an auroral arc can undergo transverse acceleration and stochastic heating. This result is very analogous to recent work regarding similar phenomena in the magnetotail (Buchner and Zelenyi, 1990; Chen and Palmadesso, 1986; Brittnacher and Whipple, 199 1). An analytic expression for the maximum arc width for which chaotic behavior is present is derived and numerically verified. We find, for example, that a 1.5-km-thick arc at LAMBDA = 65-degrees requires a minimum potential drop of 3 kV for transverse ion acceleration and heating to occur. Thicker arcs require higher potential drops for stochasticity to occur. This mechanism could be a source for conic ions.
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| 3. |
- Rothwell, P.L., et al.
(author)
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O+ phase bunching and auroral arc structure
- 1994
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 99, s. 2461-2470
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Journal article (peer-reviewed)abstract
- The equations of motion are solved for ions moving in a model electric field that corresponds to the nightside equatorial region df the magnetosphere. The model represents the poleward region of the Harang discontinuity mapped to the magnetosphere. Within this region the model electric field has a constant earthward gradient superimposed on a constant dawn-to-dusk electric field. In combination with the earthward drift motion due to the dawn-to-dusk field, the electric field gradient introduces an earthward inertia drift, which is proportional to the ion mass and therefore faster for O+ ions than for H+ ions or electrons. It is also found that the entry of the ions into the gradient region causes phase bunching and as a result ion density striations form. The striations are enhanced for more abrupt changes in the electric field gradient, a weaker magnetic field, a stronger cross-tail electric field and colder O+ ions. The first two conditions apply during the growth phase of a substorm. Using the Tsyganenko (1987) model a minimum electric field gradient value of 1 x 1O(-9) V/m(2) ((1 mV/m)/1000 km) at L = 6-7 is found. Charge neutrality requires coupling with the ionosphere through electrons moving along magnetic held lines, and such electrons may be the cause of multiple auroral arcs.
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| 4. |
- Rothwell, P.L., et al.
(author)
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PREBREAKUP ARCS - A COMPARISON BETWEEN THEORY AND EXPERIMENT
- 1991
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96, s. 13967-13975
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Journal article (peer-reviewed)abstract
- We have developed a model describing the structure of a prebreakup arc based on an ionospheric Cowling channel and its extension into the magnetosphere. A coupled two-circuit representation of the substorm current wedge is used which is locally superimposed on both westward and eastward electrojets. We find that brighter, more unstable prebreakup arcs are formed in the premidnight (southwest of the Harang Discontinuity) than in the postmidnight (northeast of the Harang Discontinuity) sector. This contributes to the observed prevalence of auroral activity in the premidnight sector. Also, our model predicts that the north-south dimensions of the current wedge in the ionosphere should vary from a few kilometers at an invariant latitude (LAMBDA) of 62-degrees to hundreds of kilometers above LAMBDA = 68-degrees. Comparison of the model results with the extensive observations of Marklund et al. (1983) for a specific arc observed just after onset shows good agreement, particularly for the magnitude of the polarization electric field and the arc size. We conclude that this agreement is further evidence that the substorm breakup arises from magnetosphere-ionosphere coupling in the near magnetosphere and that the steady state model developed here is descriptive of the breakup arc before inductive effects become dominant.
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