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| 35. |
- Sommariba, Oscar
(författare)
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Heuristic Algorithms for Combined Scheduling and Routing in Spatial TDMA Wireless Ad hoc Networks
- 2004
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Konferensbidrag (refereegranskat)abstract
- Multi-hop ad hoc wireless networking is a very attractive alternative for the communications in areas where there is a scarcity of telecommunications infrastructure. A major design issue in such networks is the formulation of the Medium Access Control (MAC) protocols. S-TDMA is a conflict-free MAC protocol thus enabling high spectral utilization, however scheduling is required. In link oriented S-TDMA the schedule specifies when particular radio links will be activated. In most wireless networks simultaneous links activation or "spatial reuse" is possible. An efficient schedule will take advantage of this reuse to ensure a high network throughput. Good scheduling is critical to network performance. Moreover, the "path finding" methods, i.e. the routing algorithm, are also critical in the design of multi-hop ad hoc wireless networks. This integrated or joint approach between routing and link scheduling is highly recommended in order to coordinates more efficiently the use of the communications resources in these networks. This paper investigates the performance gains with some heuristic algorithms for scheduling/routing in an S-TDMA ad hoc wireless networks, subject to given constraint regarding the peak transmission power ceiling per node. We introduce some routing/scheduling strategies, namely: MPRA (MinPowerpath Routing Algorithm), BMPRA (Balanced MPRA), COSRA (COmbined Scheduling & Routing Algorithm), and ARA-MHA (Advance Reuse Adaptive Minimum Hop Algorithm), and compare this strategies with MHA. The results show that when power control is used, ARA-MHA produces substantial improvement in throughput and packet delay.
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| 36. |
- Espinoza, Felix
(författare)
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Rotavirus in pediatric gastroenteritis in Nicaraguan children
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rotavirus, the most common diarrheic pathogen in children worldwide, causes approximately one third of diarrhea-associated hospitalizations and 800,000 deaths per year. To prevent the enormous health burden of rotavirus-associated disease is a global public health goal developed as well as implementation of safe and effective vaccines to be used in developing countries. We examined the epidemiology and disease burden of rotavirus diarrhea among hospitalized and outpatient children in Leon, Nicaragua, through several studies carried out from 1991 to 2003. Rotavirus was detected in 28-40% of children hospitalized for diarrhea and in 15% who were treated as outpatients. The mean age distribution of children hospitalized with rotavirus diarrhea, varied from 9.2 months in 1994 to 14 months in 2002-2003. Overall median duration of hospitalization was two days. Rotavirus was detected year-round but generally exhibited seasonal peaks during the dry months (February to June). In our material, collected during 2001 to 2003, rotavirus strains of serotype G1 P[8] were the predominant, followed by G2 P[4] and G3 P[8], G4 P[6] and 4% were uncommon strains. A shift for G types was observed; genotype G2 was the most prevalent during 2001 (70%) but decreased in 2002 when the predominating genotype became G1 (75%). The G3 genotype, which was not detected in 2001, emerged late in 2002 and was the most dominant strain in 2003 (59%). The health care costs of rotavirus diarrhea hospitalization were estimated through the register of hospital stay (bed day), the cost of the treatment and laboratory services, and additional expenses by the parents. The mean total costs including the costs paid by the family and by the Health Ministry sources were calculated to USD 117.4 per child hospitalized with rotavirus diarrhea. However, children with rotavirus negative stools spent longer time in hospital compared to children whose stools were positive (3.6 versus 2.9 days), and the calculated costs for these children rose to USD 147.9. Overall, among the total population less than 3 years of age in Nicaragua, we estimated that 2,603 cases of hospitalization due to rotavirus associated diarrhea occurs per year in Nicaragua, a disease burden which represents a cost of more than USD 270,000 from the Health care sources. If all cases of severe diarrhea are considered, including other etiologies of gastroenteritis, the total cost burden amounts to more than USD 800,000, a sum that represents around 0.6 % of the total budget of the national Health care sources. Besides, the total cost for these parents was estimated to amount to further USD 90,000. Our results confirm that rotavirus is the most important cause of severe diarrhea in Nicaragua and represent an important disease burden in hospital costs. A rotavirus, vaccine program should be of considerable benefit to prevent these severe cases.
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| 37. |
- Monterroso, David A., et al.
(författare)
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Spatial variations of b-value in the subduction zone of Central America
- 2003
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Ingår i: Geofísica Internacional. - 0016-7169. ; 42:4, s. 575-587
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Tidskriftsartikel (refereegranskat)abstract
- requency-magnitude distribution along the Mid-American Trench (MAT) has been studied by means of 2345 earthquakesduring the period 1964-1994. We used the regional MIDAS catalogue with a magnitude of completeness of 4.2. To resolve the bvalueas a function of depth (one dimensional approach), we applied vertically sliding windows containing a constant number ofevents. To obtain more details in the b distribution, we projected catalogue hypocenters in three selected regions (approximatelyGuatemala and El Salvador, Nicaragua, Costa Rica), onto planes perpendicular to the trench. The b-values were calculated insliding cylindrical volumes (two-dimensional approach) containing a constant number of earthquakes and centered at nodes of a5 km x 5 km grid. The b-value varies significantly along a large part of MAT. High b-values were identified in the upper part of theslab at depths of 80-110 km beneath Guatemala-El Salvador and at depths 130-170 km beneath Nicaragua. Anomalous (high) bvaluesin the lower part of the slab were located at depths of 50-90 km and 50-160 km beneath Guatemala-El Salvador andNicaragua, respectively. Anomalies observed at the upper part of the slab may be related to dehydration and successive increase inpore pressure in the down-going lithosphere, which may generate volcanism above the anomalies in the upper part of the slab.Anomalies on the lower surface of the Wadati-Benioff zone are likely to be associated with high thermal gradients between theslab and mantle.
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| 38. |
- Lovmar, Lovisa, 1977-
(författare)
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Methods for Analysis of Disease Associated Genomic Sequence Variation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Molecular Medicine a wide range of methods are applied to analyze the genome to find genetic predictors of human disease. Apart from predisposing disease, genetic variations may also serve as genetic markers in the search for factors underlying complex diseases. Additionally, they provide a means to distinguish between species, analyze evolutionary relationships and subdivide species into strains. The development and improvement of laboratory techniques and computational methods was a spin-off effect of the Human Genome Project. The same techniques for analyzing genomic sequence variations may be used independent of organism or source of DNA or RNA. In this thesis, methods for high-throughput analysis of sequence variations were developed, evaluated and applied. The performance of several genotyping assays were investigated prior to genotyping 4000 samples in a co-operative genetic epidemiological study. Sequence variations in the estrogen receptor alpha gene were found to be associated with an increased risk of breast and endometrial cancer in Swedish women.Whole genome amplification (WGA) enables large scale genetic analysis of sparse amounts of biobanked DNA samples. The performance of two WGA methods was evaluated using four-color minisequencing on tag-arrays. Our in-house developed assay and “array of arrays” format allow up to 80 samples to be analyzed in parallel on a single microscope slide. Multiple displacement amplification by the Φ29 DNA polymerase gave essentially identical genotyping results as genomic DNA. To facilitate accurate method comparisons, a cluster quality assessment approach was established and applied to assess the performance of four commercially available DNA polymerases in the tag-array minisequencing assay. A microarray method for genotyping human group A rotavirus (HRV) was developed and applied to an epidemiological survey of infectious HRV strains in Nicaragua. The method combines specific capture of amplified viral sequences on microarrays with genotype-specific DNA-polymerase mediated extension of capture oligonucleotides with fluorescent dNTPs.
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| 39. |
- Monterroso Juárez, David Aníbal, 1971-
(författare)
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Statistical Seismology Studies in Central America : b-value, seismic hazard and seismic quiescence
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis collects results of research applying theory and methods of statistical seismology to the seismicity of Central America, a region with a complex tectonic setting controlled by the interaction of four major plates, namely the Caribbean, Cocos, Nazca and North American plates.Three different earthquake catalogues were used for studies focused on stress in a tectonic volume, seismic hazard maps and seismicity patterns (precursors), covering the region 94ºW to 81ºW and 5ºN to 20ºN.Variations in the b-value, the parameter in Gutenberg & Richter’s equation LogN=a-bM, as a function of depth in the subduction zone were investigated. High b-values were identified in the upper part of the slab at depths of 80-110km beneath Guatemala-El Salvador and at depths 130-170km beneath Nicaragua. These anomalies may be related to the generation of volcanism occurring above them. Time dependence of the b-value was also studied. Five case studies were selected (events with MS ≥7.2) for a detailed analysis. In three out of five cases, it was possible to link b-value minima to the time of occurrence of corresponding large events.Seismic quiescence was mapped as a function of time and space by a griding technique. The characteristics of the quiescence were calculated using the statistics Z and ß and for Time Window lengths between 1 and 5 years. Five positive anomalies were found, which can be associated with large earthquakes (MS≥7.2).Finally, a Monte Carlo approach was utilized to evaluate the ground motion hazard and its uncertainties in northern Central America. A set of new seismic hazard maps exhibiting probabilistic values of peak ground acceleration (PGA) with 50%, 10%, and 5% probabilities of exceedance (PE) in 50 years is presented for a large area of northern Central America, including El Salvador and Guatemala.
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| 40. |
- Lara Perla, Claudia Elizabeth
(författare)
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Epidemiology of blood-borne viral infections : with special reference to Central America
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Viral diseases transmitted through blood and/or blood products continue to be a major health problem in developing countries. Much less is known about the distribution and transmission routes in these countries in development. The aim of the study was to compare the epidemiology and transmission routes of the human immunodeficiency virus type 1 (HIV-1), the hepatitis C virus (HCV), and the GB virus type C (GBV-C) or hepatitis G virus (HGV) in Sweden with developing countries in the Central American region. The genotypes of HCV present in Honduras were analyzed in eight patients using PCR, followed by direct sequencing of the core, envelope 2 (E2)/non-structural 1 (NS1), and NS5 regions. The major genotypes for HCV that are distributed worldwide, such as la, lb, and 3a have been found present in Honduras. To estimate the distribution of HIV-1 subtypes in Honduras an EIA assay using synthetic peptides corresponding to five of the major subtypes (A to E) was used. The Honduran HIV-1 epidemic show a similar distribution of HIV-1 subtype B as the HIV-1 epidemics in most of the developed world. The presence of the recently identified GBV-C/HGV was compared in samples from Sweden and Honduras. A total of 224 Swedish and 163 Honduran samples were analyzed for the presence of the presumed blood-borne GBV-C/HGV by PCR. Also, from both Sweden and Honduras, 44 cases and 58 cases, respectively, of suspected viral hepatitis of unknown origin were included. GBV-C/HGV RNA was detected in healthy Swedish as well as in healthy Honduran population. Likewise, GBV-C/HGV RNA was detected in Swedish and Honduran population of individuals with risk to acquiring blood borne viral infections. Analysis of the NS3 region for GBV-C of all positive samples confirmed HGV origin. The presence and distribution of GBV-C/HGV is related to known risk factors for bloodborne viral diseases in both Sweden and Honduras. Further, the importance of GBV-C/HGV in causing viral hepatitis of unknown origin is limited. To further clarify blood products as a transmission route and a possible association between GBV-C/HGV and fulminant hepatic failure (FHF) a retrospective study was performed. A panel of 58 patients clinically diagnosed with an acute or sub-acute FHF was screened for both GBV-C E2 antibodies and GBV-C/HGV RNA. In this study, GBV-C markers were present in 36% of the patients, which is higher than in healthy Swedish subjects (3%). Despite the elevated prevalence of GBV-C/HGV in patients with FHF our data suggest that in many cases the presence of GBV-C/HGV be caused by the therapy with contaminated blood products. Thus, elevated frequencies of GBV-C/HGV are to be expected in patients subjected to multiple transfusions and blood products. In July of 1997 a high number of HCV infections were diagnosed in the hemato-oncology ward in the pediatric hospital of Managua, Nicaragua. One of the major treatment strategies used for these children is the periodical administration of blood and/or blood products. A study was undertaken to try to understand the nature of the epidemic and to compare the transmission routes of HCV and GBV-C/HGV. A total of 185 patients were tested for HCV and GBV-C/HGV markers. In total, 92 (50%) out of 185 children had ongoing HCV infections. In contrast, GBV-C infection was confirmed in 20 (11 %) out of 185 children. Additionally, 100 Nicaraguan blood donors positive for anti-HCV were screened for HCV-RNA. Thirty-five blood donors were HCV RNA positive but only 12 (110/0) were GBV-C RNA positive. A panel of 73 hospital personnel, who were anti-HCV negative, were screened for both HCV RNA and GBV-C RNA. Two individuals (3%) were found to be HCV RNA positive and eight (11%) were GBV-C RNA positive. HCV and GBV-C coinfected one of these. Genotyping was performed in 35 of the children by sequence determination of a NS5 region fragment. The analysis showed that the majority of the children 34/35 were infected by HCV genotype 1a, and one child was infected by HCV of genotype lb. Fifteen of the blood donors were also genotyped: six were la, six were 3a, two were 2b and one was 2c. The present data allows for several conclusions. Collectively, treatment with contaminated blood products and the effective nosocomial transmission of HCV, which has been reported in developed countries, may help to explain the presence of this epidemic. Taken together several similarities exist between the presence and transmission of HIV-1, HCV, and GBV-C/HGV between Sweden and Central America. The subtypes of HIV-1 and HCV are seemed to follow the worldwide distribution. The role for GBV-C/HGV in various types of hepatitis remains unclear. Interestingly, the transmission route for GBV-C/HGV and HCV seem to differ. The present study highlights the importance of introducing screening for HCV at both blood banks and in hospitals in the developing world. However, screening alone would most likely not have prevented the HCV epidemic at the pediatric hospital "Manuel de Jesús Rivera", Managua, Nicaragua.
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