| 51. |
- Isaksson, Barbro, et al.
(författare)
-
Postantibiotic effect of aminoglycosides on gram-negative bacteria evaluated by a new method.
- 1988
-
Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press. - 0305-7453 .- 1460-2091. ; 22:1, s. 23-33
-
Tidskriftsartikel (refereegranskat)abstract
- The in-vitro postantibiotic effect (PAE) of amikacin, gentamicin, netilmicin and tobramycin was investigated by a bioluminescent assay of bacterial ATP. Two strains each of Escherichia coli and Pseudomonas aeruginosa were exposed for 1 h to different concentrations of the aminoglycosides. The aminoglycoside was removed by a 10(-3) dilution, and regrowth of bacteria was followed at hourly intervals by monitoring bacterial ATP. This method simplified the PAE studies and made such studies possible at high aminoglycoside concentrations. The length of the PAE was dose-dependent for all the aminoglycosides studied. The PAEs ranged between three and seven hours for all four strains at the aminoglycoside concentrations normally reached in serum during standard dosing. The long PAE of aminoglycosides, especially after exposure to high drug concentrations, constitutes an argument in favour of administering aminoglycosides in higher-than-usual doses with longer intervals between doses. This proposal is also supported by recent pharmacokinetic, bacteriological and toxicity data.
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| 52. |
- Isaksson, Barbro, et al.
(författare)
-
Postantibiotic effect of aminoglycosides on staphylococci.
- 1993
-
Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press. - 0305-7453 .- 1460-2091. ; 32:2, s. 215-222
-
Tidskriftsartikel (refereegranskat)abstract
- The postantibiotic effects (PAEs) of amikacin, gentamicin, netilmicin and tobramycin on Staphylococcus aureus and S. epidermidis were determined in vitro by a bioluminescence assay of bacterial ATP. Five strains of S. aureus and two strains of S. epidermidis were exposed for 1 h to varying concentrations of these aminoglycosides. Following removal of the antibiotics by dilution, bacterial regrowth was monitored at hourly intervals. The duration of the PAE increased with increasing aminoglycoside concentration. The mean PAEs for the five S. aureus strains ranged from 5-10 h at clinically achievable aminoglycoside concentrations (16-32 mg/L of amikacin and 4-8 mg/L of gentamicin, netilmicin and tobramycin). The results for one of the strains of S. epidermidis were similar to those observed for the S. aureus strains, while the PAEs on the other less susceptible S. epidermidis strain were shorter (0.5-2.5 h). For comparison, two of the S. aureus strains were exposed for 1 and 2 h to a range of concentrations of dicloxacillin (0.25-32 mg/L); this agent induced a much shorter PAE (0-2.3 h). It may be important to take account of the PAE when designing dosing regimens.
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| 53. |
- Isaksson, Barbro, et al.
(författare)
-
Synergic post-antibiotic effect of amikacin in combination with beta-lactam antibiotics on gram-negative bacteria.
- 1991
-
Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press. - 0305-7453 .- 1460-2091. ; 28:1, s. 25-34
-
Tidskriftsartikel (refereegranskat)abstract
- The post-antibiotic effect (PAE) of amikacin alone and in combination with ceftazidime, ceftriaxone and piperacillin was studied for two strains each of Pseudomonas aeruginosa and Serratia marcescens using a bioluminescent assay of bacterial ATP. Two models were used for combining beta-lactam antibiotics and amikacin: in one model the cultures were incubated with 32 mg/L of ceftazidime, 128 mg/L of ceftriaxone or 32 mg/L of piperacillin for 1 h. Different concentrations of amikacin (0.5-64 mg/L) were then added. Incubation of the combinations continued for one more hour. The antibiotics were eliminated by dilution. In the second model tested, one strain of S. marcescens was simultaneously exposed to amikacin and a beta-lactam antibiotic for 2 h. The PAEs produced by the drugs in combination were longer than the sum of the individual effects of the drugs when they were used alone. Results were equally good with both models. A synergic PAE was also found with amikacin concentrations close to the MIC in combination with low concentrations of ceftazidime, ceftriaxone and piperacillin.
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| 54. |
- Isaksson, Barbro, et al.
(författare)
-
Synergistic post-antibiotic effect of amikacin and beta-lactam antibiotics on Enterococcus faecalis.
- 1991
-
Ingår i: Journal of Antimicrobial Chemotherapy. - : Oxford University Press. - 0305-7453 .- 1460-2091. ; 27, s. 9-14
-
Tidskriftsartikel (refereegranskat)abstract
- The in-vitro post-antibiotic effect (PAE) of amikacin alone and in combination with ceftazidime, ceftriaxone and piperacillin was studied for two strains of Enterococcus faecalis using a bioluminescent assay of bacterial ATP. The two strains of E. faecalis were resistant to amikacin, ceftazidime and ceftriaxone but sensitive to piperacillin. The bacterial cultures were incubated with the beta-lactam antibiotics for 1 h and concentrations of amikacin between 2-64 mg/l were then added. Thereafter, incubation continued with the combinations for one more hour. After dilution, regrowth was monitored by measuring bacterial ATP every hour. Increasing concentrations of amikacin (2-64 mg/l), ceftazidime (8-32 mg/l) and ceftriaxone (32-128 mg/l) resulted in little or no PAE (0-0.3 h) on these strains. PAEs of 0.5 to 1.6 h resulted from exposure to piperacillin (4-32 mg/l). In combination amikacin and piperacillin increased the PAE to 5.5 h. A synergistic PAE was also seen when the enterococci were exposed to amikacin combined with ceftazidime or ceftriaxone in concentrations close to the MICs of the latter antibiotics.
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| 55. |
- Isaksson, Lennart, et al.
(författare)
-
A Fuzzy Set Theory Based Method to Discover Transmissions in Wireless Personal Area Networks
- 2006
-
Konferensbidrag (refereegranskat)abstract
- The complexity within a Wireless Personal Area Network (WPAN) increases. Several technologies have to share the same radio spectrum. In this paper we take a look at the 2.4 GHz Industrial Scientific and Medical (ISM)-band. This paper discusses a method of selecting the best wireless channel within Wireless Local Area Network (WLAN) when several technologies could be used in the same WPAN range of the needed access point. The issue is to keep away from already occupied channels. The method is divided into four steps: the passive probing of the power level detecting IEEE 802.15.4 (ZigBee) channels using a new and affordable hardware, the transformation of the probed data to a linguistic level using Fuzzy Set Theory (FST), the classification of the data, and finally the sorting and selection of channels based on whose power levels.
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| 56. |
- Isaksson, Lennart, et al.
(författare)
-
Application-Perceived Throughput Process in Wireless Systems
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Motivated by the central role and the importance of network throughput for the performance of networked applications and thus for user experience, this paper investigates the process of user-perceived throughput. This throughput is measured on rather small time scales and interpreted with aid of summary statistics, histograms and autocorrelation coefficients. The results including GPRS, UMTS and WLAN measurements reveal a clear influence of the network, seen from variations of application-perceived throughput on the one-second time scale, which has to be considered when choosing the right kind of network for a specific task. The different statistical metrics considered will later be used in our research to maintain the QoS of the service decided by the user. While theoretical throughputs are yielded as expected in UMTS, both GPRS and WLAN do not reach the promised throughput values.
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| 57. |
- Isaksson, Lennart
(författare)
-
High-resolution measurement of the ¹⁶O(γ,pn) reaction
- 1996
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The 16O(gamma,pn) reaction has been measured with a resolution high enough to resolve individual low-lying states in the residual 14N nucleus. The relative population of the states provides detailed information about the quantum numbers of the proton-neutron pairs on which photons are absorbed. Partial cross-sections, available to the acceptance of the detector system, have been extracted for the individual states, and compared to a recent calculation based on absorption on one-pion exchange currents and the Delta-resonance current. The experiment was performed at the Maxlab accelerator laboratory in Lund, Sweden, using tagged photons at an energy of 67-76 MeV. The proton detector angular range was 60-100 degrees and the corresponding number for the neutron detector was 81-103 degrees. A missing-energy resolution of 1.5 MeV was obtained. The relative population of the states in the residual 14N nucleus indicates that the (gamma,pn) reaction takes place predominantly on proton-neutron pairs coupled to (J^pi,T) = (1^+,0), where J is the total angular momentum of the pair, pi is the parity and T is the isospin. The cross-section for absorption on (0^+,1) pairs is strongly suppressed. Furthermore, the relative population of the states indicates that both L=0 and L=2 pairs participate in the reaction, where L is the angular momentum of the center-of-mass of the pair.
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| 58. |
- Isaksson, Lennart
(författare)
-
Improved Performance of Bluetooth with Focus on Ad-Hoc Applications
- 2004
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The number of devices making use of Bluetooth cable-replacement technology has rapidly increased in numbers thanks to the amount of implementations in cellular telephones, Personal Digital Assistants (PDAs), etc. Instead of the point-to-point technique used today the wireless community demands more sophisticated solutions to transmit information between two devices, e.g. using a chat program within an ad-hoc network. However, Bluetooth provides neither a routing protocol, nor is the slave/slave bridge, which is an important enabler for point-to-multipoint communication in so-called scatternets, implemented in hardware. Another issue relates to the time-to-connect which determines the usability of Bluetooth in scenarios where the units move around. In order to build research on these topics on trustworthy ground, we first address the validation of a Bluetooth simulation model, implementing the Frequency Hopping Spread Spectrum (FHSS) technique of Bluetooth version 1.1 in a correct way. A potential source of problems in reference simulation models has been identified and corrections are described. Next, an improvement is presented for the pseudo random hop sequence regarding the distribution of frequencies used in the Adapted Channel Hopping (ACH) scheme for Bluetooth version 1.2. Further, the impact of the random backoff boundary, which determines the duration of the inquiry procedure and thus of the time-to-connect, is studied by simulation. Obviously, the settings of this parameter contained in the specification leads to suboptimal behaviour. In this thesis, a lower random backoff boundary parameter is suggested, which yields much faster time-to-connect. Finally, the Modified Reverse Path Forwarding (MRPF) routing algorithm for Bluetooth is proposed. This algorithm reduces the amount of connections needed to transmit Asynchronous Connection Less (ACL) data packets as compared to the standard RPF, at the cost of additional overhead. Altogether, especially with the proposed improvements of Bluetooth performance, this technology can be considered to be well suited for nomadic scenarios.
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| 59. |
- Isaksson, Lennart, et al.
(författare)
-
Improved Time to Connect for Bluetooth
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Bluetooth has from its beginning used Frequency Hopping (FH) from version 1.0A to the current version 1.2. The so-called selection box uses a complex scheme to calculate the next correct frequency in time. This makes transmissions between Bluetooth devices both robust and secure. Several attempts have been carried out to improve the time to connect, due to the relatively high time to connect given by the Bluetooth specification. Many have not fully understood the FH for Bluetooth and have therefore suggested sub-optimized solutions to improve the time to connect. In this paper, a presentation of the problem that causes the poor time to connect performance is given. This knowledge is needed for an improvement of the time to connect for Bluetooth. To accomplish a reduction of the time to connect by a factor of 100, three main parameters have to be changed: First, the A-train and B-train should be switched directly after each other. Second, the phase should be switched faster, which is based on the clock. Finally, a reduction of the random backoff parameter needs to be considered. These changes, together with other parameters, like time out values, have to be changed/reduced accordingly. Together with these changed parameters a simulation of the time to connect for Bluetooth is presented.
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| 60. |
- Isaksson, Lennart, et al.
(författare)
-
On-Demand Ad Hoc Routing with Modified Reverse Path Forwarding for Bluetooth
- 2004
-
Konferensbidrag (refereegranskat)abstract
- In an ad hoc network connection establishment is done to secure a path for routing packets from source to destination. This path is then maintained to secure further transmissions. In the case of Wireless Personal Area Networks (WPAN) which are more flexible, this is not usable. This is especially the case for Bluetooth. Some constraints in Bluetooth demands a more flexible on-demand ad hoc network compared to other types of ad hoc network protocols. Initially we found that creating a scatternet is not practically possible using Bluetooth version 1.1. The slave/slave bridge is not implemented into the hardware to create a scatternet. In this paper, we present a modified version of the Reverse Path Forwarding (RPF) algorithm to make it suitable for Bluetooth routing. With an on-demand ad hoc network solution together with the modified RPF algorithm we present a suitable solution for Bluetooth packets to be routed in a flexible ad hoc network. To be able to test the modified RPF and the on-demand ad hoc network, a test platform has also been developed.
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