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Karl-Ludwig Besser,Eduard A. Jorswieck,Justin P. Coon 한국통신학회 2024 Journal of communications and networks Vol.26 No.4
We consider a two-ray ground reflection scenario with unknown distance between transmitter and receiver. By utilizing two frequencies in parallel, we can mitigate possible destructive interference and ensure ultra-reliability with only very limited knowledge at the transmitter. In order to achieve this ultra-reliability, we optimize the frequency spacing such that the worst-case receive power is maximized. Additionally, we provide an algorithm to calculate the optimal frequency spacing. Besides the receive power, we also analyze the achievable rate and outage probability. It is shown that the frequency diversity scheme achieves a significant improvement in terms of reliability over using a single frequency. In particular, we demonstrate the effectiveness of the proposed approach by a numerical simulation of an unmanned aerial vehicle (UAV) flying above flat terrain.
E.A. Lennon,A.A. Burke,R.S. Besser 한국물리학회 2012 Current Applied Physics Vol.12 No.4
Microhollow cathode discharge (MHCD) devices generate microplasmas with high electron densities and reactive species, making them a prospective hydrocarbon reforming technology. Here we report on the electrical phenomena resulting from MHCD devices with elongated trenches using argon at atmospheric pressure and room temperature. Devices that were 100 mm wide, 100 mm deep, and 1 cm long exhibited self-pulsing current during constant voltage DC power application ranging from 0 mA to 32 mA. The capacitances for MHCDs with trenches 25, 100, and 250 mm wide were estimated to be 68, 70, and 33 mF respectively. A current-limited DC supply prevented self-pulsing, and resulted in abnormal, normal, or negative differential resistance (NDR), i.e. hollow cathode, operating modes. The NDR state manifested at lower current limits and occurred when the microplasma in the trench was discontinuous. Simulations from a corresponding, empirically determined circuit model showed larger total average power consumption (including the ballast resistance) during pulsed inputs (5.61e31.08 W) in comparison to constant voltage inputs (<1 W). These findings advance the development of these MHCDs for microplasma reforming applications, providing insights into operational modes and power consumption estimates critical to understanding the overall efficiency in the context of a future microplasma reforming system.
Phenotypic Diversity of Escherichia coli O157:H7 Strains Associated with the Plasmid O157
Ji Youn Lim,홍준배,Haiqing Sheng,Smriti Shringi,Thomas E. Besser,Carolyn J. Hovde,Rajinder Kaul 한국미생물학회 2010 The journal of microbiology Vol.48 No.3
Escherichia coli O157:H7, a food-borne pathogen, causes hemorrhagic colitis and the hemolytic-uremic syndrome. A putative virulence factor of E. coli O157:H7 is a 60-MDa plasmid (pO157) found in 99% of all clinical isolates and many bovine-derived strains. The well characterized E. coli O157:H7 Sakai strain (Sakai) and its pO157-cured derivative (Sakai-Cu) were compared for phenotypic differences. Sakai-Cu had enhanced survival in synthetic gastric fluid, did not colonize cattle as well as wild-type Sakai, and had unchanged growth rates and tolerance to salt and heat. These results are consistent with our previous findings with another E. coli O157:H7 disease outbreak isolate ATCC 43894 and its pO157-cured (43894-Cu). However, despite the essentially sequence identical pO157 in these strains, Sakai-Cu had changes in antibiotic susceptibility and motility that did not occur in the 43894-Cu strain. This unexpected result was systematically analyzed using phenotypic microarrays testing 1,920 conditions with Sakai, 43894, and the plasmid-cured mutants. The influence of the pO157 differed between strains on a wide number of growth/survival conditions. Relative expression of genes related to acid resistance (gadA, gadX, and rpoS) and flagella production (fliC and flhD) were tested using quantitative real-time PCR and gadA and rpoS expression differed between Sakai-Cu and 43894-Cu. The strain-specific differences in phenotype that resulted from the loss of essentially DNA-sequence identical pO157 were likely due to the chromosomal genetic diversity between strains. The O157:H7 serotype diversity was further highlighted by phenotypic microarray comparisons of the two outbreak strains with a genotype 6 bovine E. coli O157:H7 isolate, rarely associated with human disease.
Bae, Wonki,Hancock, Dale D.,Call, Douglas R.,Park, Yong Ho,Berge, Anna Catharina B.,Finger, Regina M.,Sischo, William M.,Besser, Thomas E. Elsevier 2007 Veterinary microbiology Vol.122 No.3-4
<P><B>Abstract</B></P><P>The purpose of this study was to investigate the genetic similarity of <I>Campylobacter jejuni</I> and <I>Campylobacter coli</I> with similar antimicrobial resistance phenotypes, isolated from cattle on different farms and at different times, in order to evaluate the possible existence of disseminated antimicrobial resistant clones. PFGE after <I>Sma</I>I and <I>Kpn</I>I restriction identified 23 and 16 distinct PFGE patterns among 29 <I>C. jejuni</I> and 66 <I>C. coli</I> isolates, respectively. In <I>C. coli</I>, 51 (77%) of the resistant isolates demonstrated one of the four indistinguishable PFGE patterns, whereas only 24% doxycycline resistant <I>C. jejuni</I> shared one of the two indistinguishable PFGE patterns. The genetic mechanisms of resistance were homogeneous within and between these clonal types. Genetically indistinguishable (clonal) groups of <I>C. coli</I> accounted for most <I>Campylobacter</I> sp. with multiple antimicrobial resistance observed in this study, consistent with a role for clonal dissemination in the epidemiology of resistance in this species.</P>