New Graph Model for Channel Assignment in Ad Hoc Wireless Networks

The channel assignment problem in ad hoc wireless networks is investigated. The problem is to assign channels to hosts in such a way that interference among hosts is eliminated and the total number of channels is minimised. Interference is caused by direct collisions from hosts that can hear each other or indirect collisions from hosts that cannot hear each other, but simultaneously transmit to the same destination. A new class of disk graphs (FDD: interFerence Double Disk graphs) is proposed that include both kinds of interference edges. Channel assignment in wireless networks is a vertex colouring problem in FDD graphs. It is shown that vertex colouring in FDD graphs is NP-complete and the chromatic number of an FDD graph is bounded by its clique number times a constant. A polynomial time approximation algorithm is presented for channel assignment and an upper bound 14 on its performance ratio is obtained. Results from a simulation study reveal that the new graph model can provide a more accurate estimation of the number of channels required for collision avoidance than previous models

Thermodynamic model of electric-field-induced pattern formation in binary dielectric fluids

An electric-field-induced phase transition and pattern formation in a binary dielectric fluid layer are studied using a coarse-grained free-energy functional. The electrostatic part of the free energy is a nonlinear functional of the dielectric function, which depends in turn on the local colloidal concentration. We determine the phase coexistence curve and find that beyond a critical electric field the system phase separates. Accompanying the phase separation are patterns similar to those observed in a spinodal decomposition of an ordinary binary fluid. The temporal evolution of the phase separating patterns are discussed both analytically and numerically by integrating a Cahn-Hilliard type of equation

Development of a Queue Warning System Utilizing ATM Infrastructure System Development and Field-Testing

MnDOT has already deployed an extensive infrastructure for Active Traffic Management (ATM) on I-35W and I-94 with plans to expand on other segments of the Twin Cities freeway network. The ATM system includes intelligent lane control signals (ILCS) spaced every half mile over every lane to warn motorists of incidents or hazards on the roadway ahead. This project developed two separate systems that can identify lane-specific shockwave or queuing conditions on the freeway and use existing ILCS to warn motorists upstream for rear-end collision prevention. The two systems were field tested at two locations in the ATM equipped network that have a high frequency of rear- end collisions. These locations experience significantly different traffic-flow conditions, allowing for the development and testing of two different approaches to the same problem. The I-94 westbound segment in downtown Minneapolis is known for its high crash rate due to rapidly evolving shockwaves while the I-35W southbound segment north of the TH-62 interchange experiences longstanding queues extending into the freeway mainline. The Minnesota Traffic Observatory developed the I-94 Queue Warning system while the University of Michigan, under contract, developed the I-35W system. Prior to the I-94 installation, based on data collected in 2013, there were 11.9 crashes per VMT and 111.8 near crashes per VMT. In the first three months of the system’s deployment, event frequency reduced to 9.34 crashes per million vehicle miles of travel (MVMT) and 51.8 near crashes per MVMT, a 22% decrease in crashes and a 54% decrease in near crashes. The I-35W system did not undergo a similarly thorough evaluation, but for most of the lane segments involved, it showed that queue warning messages help reduce the speed variance near the queue locations and the speed difference between upstream and downstream locations. This also implicated a satisfactory level of compliance rate from travelers

Evolution of hydrogen and helium co-implanted single-crystal silicon during annealing

H+H+ was implanted into single-crystal silicon with a dose of 1×1016/cm21×1016/cm2 and an energy of 30 KeV, and then He+He+ was implanted into the same sample with the same dose and an energy of 33 KeV. Both of the implantations were performed at room temperature. Subsequently, the samples were annealed in a temperature range from 200 to 450 °C450 °C for 1 h. Cross-sectional transmission electron microscopy, Rutherford backscattering spectrometry/channeling, elastic recoil detection, and high resolution x-ray diffraction were employed to characterize the strain, defects, and the distribution of H and He in the samples. The results showed that co-implantation of H and He decreases the total implantation dose, with which the surface could exfoliate during annealing. During annealing, the distribution of hydrogen did not change, but helium moved deeper and its distribution became sharper. At the same time, the maximum of the strain in the samples decreased a lot and also moved deeper. Furthermore, the defects introduced by ion implantation and annealing were characterized by slow positron annihilation spectroscopy, and two positron trap peaks were found. After annealing, the maximum of these two peaks decreased at the same time and their positions moved towards the surface. No bubbles or voids but cracks and platelets were observed by cross-sectional transmission electron microscopy. Finally, the relationship between the total implantation dose and the fraction of hydrogen in total implantation dose was calculated. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70387/2/JAPIAU-90-8-3780-1.pd

Defect and strain in hydrogen and helium coimplanted single-crystal silicon

In this paper we studied the processes of blistering and exfoliation on the surface of crystal silicon, the evolution of defects/strains in the crystal silicon caused by hydrogen and helium coimplantation during annealing, and the formation of platelets and bubbles in the crystal. It is shown that H + and He + coimplantation produces a synergistic effect, which greatly decreases the total implantation dose, compared with either just H + or He + implantation. We also present the effect of coimplantation and analyse the different roles of H and He in the process of exfoliation during annealing. It seems that the essential role of hydrogen is to interact chemically with the defects in the silicon and create H-stabilized platelets, while the role of helium is to effuse into these platelets and exert a pressure on the inner surface of these platelets. The damage caused by coimplantation is lower than by hydrogen implantation (at the dose that exfoliation requires).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48907/2/d10102.pd

Comparison between the different implantation orders in H + and He + coimplantation

H + and He + were implanted into single crystals in different orders (H + first or He + first). Subsequently, the samples were annealed at different temperatures from 200 °C to 450 °C for 1 h. Cross sectional transmission electron microscopy, Rutherford backscattering spectrometry and channelling, elastic recoil detection were employed to characterize the defects and the distribution of H and He in the samples. Furthermore, the positron traps introduced by ion implantation and annealing were characterized by slow positron annihilation spectroscopy. Both orders in the coimplantation of H and He have the ability to decreases the total implantation dose after annealing. No bubbles or voids but cracks and platelets, were observed by cross sectional transmission electron microscopy. The different implantation orders affect the density of interstitial atoms and positron traps.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48910/2/d10406.pd

Extensive transmission of isoniazid resistant M. tuberculosis and its association with increased multidrug-resistant TB in two rural counties of eastern China: A molecular epidemiological study

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to investigate the molecular characteristics of isoniazid resistant <it>Mycobacterium tuberculosis </it>(MTB), as well as its contribution to the dissemination of multi-drug resistant TB (MDR-TB) in rural areas of eastern China.</p> <p>Methods</p> <p>A population-based epidemiological study was conducted in two rural counties of eastern China from 2004 to 2005. In total, 131 isoniazid resistant MTB isolates were molecularly characterized by DNA sequencing and genotyped by IS<it>6110 </it>restriction fragment length polymorphism (RFLP) and spoligotyping.</p> <p>Results</p> <p>The <it>katG</it>315Thr mutation was observed in 74 of 131 isoniazid resistant isolates and more likely to be MDR-TB (48.6%) and have mutations in <it>rpoB </it>gene (47.3%). Spoligotyping identified 80.2% of isoniazid resistant MTB isolates as belonging to the Beijing family. Cluster analysis by genotyping based on IS<it>6110 </it>RFLP, showed that 48.1% isoniazid resistant isolates were grouped into 26 clusters and <it>katG</it>315Thr mutants had a significantly higher clustering proportion compared to those with <it>katG </it>wild type (73%.vs.18%; OR, 12.70; 95%CI, 6.357-14.80). Thirty-one of the 53 MDR-TB isolates were observed in 19 clusters. Of these clusters, isoniazid resistance in MDR-TB isolates was all due to the <it>katG</it>315Thr mutation; 18 clusters also contained mono-isoniazid resistant and other isoniazid resistant isolates.</p> <p>Conclusions</p> <p>These results highlighted that isoniazid resistant MTB especially with <it>katG</it>315Thr is likely to be clustered in a community, develop extra resistance to rifampicin and become MDR-TB in Chinese rural settings.</p

Transmission Pattern of Drug-Resistant Tuberculosis and Its Implication for Tuberculosis Control in Eastern Rural China

OBJECTIVE: Transmission patterns of drug-resistant Mycobacterium tuberculosis (MTB) may be influenced by differences in socio-demographics, local tuberculosis (TB) endemicity and efficaciousness of TB control programs. This study aimed to investigate the impact of DOTS on the transmission of drug-resistant TB in eastern rural China. METHODS: We conducted a cross-sectional study of all patients diagnosed with drug-resistant TB over a one-year period in two rural Chinese counties with varying lengths of DOTS implementation. Counties included Deqing, with over 11 years' DOTS implementation and Guanyun, where DOTS was introduced 1 year prior to start of this study. We combined demographic, clinical and epidemiologic information with IS6110-based restricted fragment length polymorphism (RFLP) and Spoligotyping analysis of MTB isolates. In addition, we conducted DNA sequencing of resistance determining regions to first-line anti-tuberculosis agents. RESULTS: Of the 223 drug-resistant isolates, 73(32.7%) isolates were identified with clustered IS6110RFLP patterns. The clustering proportion among total drug-resistant TB was higher in Guanyun than Deqing (26/101.vs.47/122; p,0.04), but not significantly different among the 53 multidrug-resistant isolates (10/18.vs.24/35; p,0.35). Patients with cavitary had increased risk of clustering in both counties. In Guanyun, patients with positive smear test or previous treatment history had a higher clustering proportion. Beijing genotype and isolates resistant to isoniazid and/or rifampicin were more likely to be clustered. Of the 73 patients with clustered drug-resistant isolates, 71.2% lived in the same or neighboring villages. Epidemiological link (household and social contact) was confirmed in 12.3% of the clustered isolates. CONCLUSION: Transmission of drug-resistant TB in eastern rural China is characterized by small clusters and limited geographic spread. Our observations highlight the need for supplementing DOTS with additional strategies, including active case finding at the village level, effective treatment for patients with cavities and drug susceptibility testing for patients at increased risk for drug-resistance