| 1. |
- Elfsberg, Mattias, et al.
(författare)
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Experimental studies on a coaxial vircator, designed for operation in TE11 mode
- 2011
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Ingår i: Proc. of Pulse Power Conference (PPC 2011). ; , s. 811-814
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Konferensbidrag (refereegranskat)abstract
- Experiments on a coaxial vircator have been performed. A vircator is a narrow band high power microwave source without any external generated magnetic field [1]. A coaxial vircator is an advantageous design of a microwave radiation source for a compact HPM-system. With a limited size and outer diameter it is possible to use a larger emitting area compared to an axial design. A conventional coaxial vircator will generate the radiation in TM01 mode, due to its geometrical properties. For a compact HPM-system, radiation in TE11 mode is preferred when the radiated energy needs to be focused on a specific target. For operation in TE11 mode a sectioned emitter can be used rather than a circumcircular. The efficiency of the vircator can be greatly improved by optimizing the geometry of the vircator housing. The impedance of the pulsed power supply driving the vircator and the impedance of the vircator, depending on the A-K gap and amount of emitting material, is also important for maximizing the vircator efficiency. For the experiments reported on, the vircator was driven by a 500 kV/500 J compact Marx generator that can be operated repetitively at 10 Hz. For these experiments, the Marx generator was operating in single shot mode. During the experiments presented here, a couple of geometrical features were varied as well as the applied voltage. Their influence on the radiated field strength, dominating frequency and bandwidth are reported on and discussed.
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| 2. |
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| 3. |
- Möller, Cecilia, et al.
(författare)
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Experimental Studies of the Influence of a Resonance Cavity in an Axial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:6, s. 1318-1324
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on an axial virtual-cathode oscillator (vircator) with a resonance cavity enclosing the virtual cathode are reported. The vircator is driven by a repetitive Marx generator operating in a single-shot mode. To be able to separate different radiation mechanisms, the design of the vircator allows adjustment of the cavity depth as well as the way microwave radiation is extracted. The microwave radiation is measured with a pair of free-field B-dot sensors. The maximum field strengths were registered when the bandwidth was very narrow.
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| 4. |
- Möller, Cecilia, et al.
(författare)
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Experimental study of a vircator with premodulated electron beam
- 2011
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Ingår i: Proc. of Pulse Power Conference (PPC 2011)”, Chicago,USA, June 2011.. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 815-818
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Konferensbidrag (refereegranskat)abstract
- An initial experimental study of a vircator where a feedback mechanism is used to premodulate the electron beam has been performed. The anode-cathode gap distance and the applied voltage were varied and their influence on the frequency content and field strength of the generated microwave pulse are investigated and compared with particle in cell simulations. The frequency content of the microwave radiation was in good agreement between experiments and simulations. The vircator was very narrow banded at 2 GHz.
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| 5. |
- Möller, Cecilia, et al.
(författare)
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Proof of Principle Experiments on Direct Generation of the TE11 Mode in a Coaxial Vircator
- 2010
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Ingår i: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 38:1, s. 26-31
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Tidskriftsartikel (refereegranskat)abstract
- Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the TE11 mode and inhibit growth of the TM01 mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8 '' vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the TE11 mode.
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| 6. |
- Nyholm, Dag, et al.
(författare)
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Circadian rhythmicity in levodopa pharmacokinetics in patients with Parkinson disease
- 2010
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Ingår i: Clinical neuropharmacology. - 0362-5664 .- 1537-162X. ; 33:4, s. 181-185
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES:: The purpose of this study was to compare daytime and nighttime plasma pharmacokinetics (PK) of levodopa in patients with Parkinson disease. METHODS:: Four-hour plasma profiles of levodopa were captured in 8 patients with Parkinson disease after the second daily levodopa dose and after the identical dose at bedtime. Patients were fasting 2 hours before and 2 hours after dose intakes, except standardized amounts of tap water. Body position was upright during daytime testing and supine during nighttime testing. Four patients were additionally tested at daytime in supine position. RESULTS:: The absorption rate was significantly delayed at nighttime dosing. The time at which the maximum peaks occurred was delayed from 25 (15-240) to 105 (20-240) minutes, respectively. Maximum concentrations were significantly lower at night, but the plasma exposure (area under the curve, 0-4 hours) was unaffected. Supine daytime plasma PK was in between day and night results. CONCLUSIONS:: There is a slower absorption rate of levodopa during nighttime, probably related to delayed gastric emptying. However, the extent of absorption and bioavailability were unaffected. As the effect of posture on plasma PK was less than the effect of nighttime, this study suggests that the circadian rhythm has a pronounced effect on gastric emptying and absorption rate. Nevertheless, body position may also be an important factor, and it can be recommended that levodopa tablets be taken in upright position that probably should be sustained for at least 30 minutes.
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| 7. |
- Nyholm, Dag, et al.
(författare)
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Complexity of Motor Response to Different Doses of Duodenal Levodopa Infusion in Parkinson Disease
- 2012
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Ingår i: Clinical neuropharmacology. - 0362-5664 .- 1537-162X. ; 35:1, s. 6-14
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Forskningsöversikt (refereegranskat)abstract
- OBJECTIVE: The aim was to elaborately describe individual pharmacokinetic-pharmacodynamic profiles in patients with difficult-to-treat dyskinesias treated with levodopa/carbidopa intestinal gel infusion. METHODS: A nonrandomized, partly blinded, investigator-initiated trial was conducted in 5 patients with idiopathic Parkinson disease who were difficult to keep in "on" state without dyskinesia. Levodopa/carbidopa intestinal gel (Duodopa) doses of 80% to 120% of individually and clinically optimized dosage were infused during five 4-hour periods. Pharmacokinetic profiling, blinded assessment of video recordings, and objective movement analysis were applied every 20 to 30 minutes. RESULTS: Individual correlations between plasma levodopa concentrations and corresponding motor scores 20 to 30 minutes after the sampling time were significant in all patients (P < 0.05 and P < 0.001). Motor scores were generally stable during the 4-hour periods. The objective test revealed that motor performance was faster the more dyskinetic the patients were. Mean individual Treatment Response Scale scores were positive in 24 of the 25 steady-state periods. Dystonia was always combined with choreic dyskinesias. CONCLUSIONS: Motor response from different doses of levodopa/carbidopa intestinal gel is in a broad sense predictable even in dyskinetic patients although major interindividual differences in dose requirement, plasma levels, and motor response are found. That motor performance was faster the more dyskinetic the patients were implies that motor performance may be better with moderate dyskinesia than with mild dyskinesia. This may explain why patients with persistent dyskinesias choose to keep their doses above the dyskinesia threshold. There is no ideal therapeutic window in such patients, but levodopa infusion offers stable motor response.
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| 8. |
- Nyholm, Dag, et al.
(författare)
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Frequent administration of levodopa/carbidopa microtablets vs levodopa/carbidopa/entacapone in healthy volunteers
- 2013
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Ingår i: Acta Neurologica Scandinavica. - : Hindawi Limited. - 0001-6314 .- 1600-0404. ; 127:2, s. 124-132
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES:An oral dispersible microtablet formulation of levodopa/carbidopa 5/1.25 mg (LC-5) was developed for individualized repeated dosing. The aim was to compare pharmacokinetic profiles of LC-5 and levodopa/carbidopa/entacapone (LCE).MATERIALS AND METHODS:A randomized, crossover study was carried out in 11 healthy subjects. Plasma concentrations of levodopa, carbidopa and 3-O-methyldopa were determined after intake of 300 mg levodopa during the day, either as three intakes of 100/25/200 mg LCE or as a morning dose of 75/18.25 mg followed by five repeated doses of 45/11.25 mg LC-5.RESULTS:Repeated dosing (2.4-hourly) with LC-5 microtablets compared to LCE (6-hourly) avoided long periods with low plasma levodopa levels. Time to maximum plasma concentrations was significantly shorter for LC-5. LC-5 showed lower fluctuation index (FI) in plasma compared to LCE (ANOVA P = 0.0028). FI for dose 2-5 was on average 1.26 for levodopa in LC-5, and 2.23 for dose 1-2 of LCE. The ratio between the two mean FI:s is 0.565; that is, LC-5 gave nearly half the FI as compared to LCE.CONCLUSIONS:Fractionation of levodopa with LC-5 into small, frequent administrations as compared to standard administrations of LCE decreased the FI in plasma for both levodopa and carbidopa by nearly half.
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| 9. |
- Nyholm, Dag, et al.
(författare)
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Pharmacokinetics of levodopa/carbidopa microtablets versus levodopa/benserazide and levodopa/carbidopa in healthy volunteers
- 2012
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Ingår i: Clinical neuropharmacology. - 0362-5664 .- 1537-162X. ; 35:3, s. 111-117
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To compare bioavailability and pharmacokinetics of single doses of 3 different levodopa formulations given orally in healthy volunteers. Two marketed formulations, standard levodopa/carbidopa, 100/25 mg (LC-100), and dispersible levodopa/benserazide, 100/25 mg (LB-100), were used as reference formulations for a newly developed dispersible microtablet formulation of levodopa/carbidopa, 5/1.25 mg (LC-5). The microtablets are intended for individualized dosing of levodopa/carbidopa in Parkinson disease by means of an electronic dose dispenser with a built-in diary for symptom registration. METHODS: A single-dose, open, randomized, 3-way crossover study was performed in 19 healthy subjects. Concentrations of levodopa, carbidopa, and the metabolite 3-O-MD in plasma were determined after intake of 100 mg of levodopa, that is, one tablet of reference formulations and 20 microtablets of the new formulation. RESULTS: The LC-5 microtablets were bioequivalent to the LC-100 tablets in area under the curve (AUC) and maximum concentration in plasma (Cmax) for levodopa, and to the LB-100 tablets in AUC. The dispersible levodopa/benserazide formulation showed earlier time to Cmax and significantly higher Cmax for levodopa in plasma compared to the microtablets. Carbidopa showed larger interindividual variation in AUC and Cmax than levodopa, and the bioequivalence comparison LC-5/LC-100 for this compound did not reach the target. Nevertheless, comparison of 3-O-MD levels for LC-5/LC-100, assuming proportionality to levodopa levels, demonstrated bioequivalence. CONCLUSIONS: The new levodopa/carbidopa microtablets had a pharmacokinetic profile that would allow for a convenient switch of therapy from standard tablets. Frequent dose administration of levodopa/carbidopa microtablets with an electronic dose dispenser might offer an optimal oral drug delivery in Parkinson disease.
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| 10. |
- Nyholm, Dag, et al.
(författare)
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Rörelsestörningar
- 2012
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Ingår i: Neurologi. - Liber : Liber.
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Bokkapitel (populärvet., debatt m.m.)
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