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| 2. |
- Brend, Tim, et al.
(författare)
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Multiple levels of transcriptional and post-transcriptional regulation are required to define the domain of Hoxb4 expression
- 2003
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Ingår i: Development. - : The Company of Biologists. - 0950-1991 .- 1477-9129. ; 130:12, s. 2717-2728
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Tidskriftsartikel (refereegranskat)abstract
- Hox genes are key determinants of anteroposterior patterning of animal embryos, and spatially restricted expression of these genes is crucial to this function. In this study, we demonstrate that expression of Hoxb4 in the paraxial mesoderm of the mouse embryo is transcriptionally regulated in several distinct phases, and that multiple regulatory elements interact to maintain the complete expression domain throughout embryonic development. An enhancer located within the intron of the gene (region C) is sufficient for appropriate temporal activation of expression and the establishment of the correct anterior boundary in the paraxial mesoderm (somite 6/7). However, the Hoxb4 promoter is required to maintain this expression beyond 8.5 dpc. In addition, sequences within the 3' untranslated region (region B) are necessary specifically to maintain expression in somite 7 from 9.0 dpc onwards. Neither the promoter nor region B can direct somitic expression independently, indicating that the interaction of regulatory elements is crucial for the maintenance of the paraxial mesoderm domain of Hoxb4 expression. We further report that the domain of Hoxb4 expression is restricted by regulating transcript stability in the paraxial mesoderm and by selective translation and/or degradation of protein in the neural tube. Moreover, the absence of Hoxb4 3'-untranslated sequences from transgene transcripts leads to inappropriate expression of some Hoxb4 transgenes in posterior somites, indicating that there are sequences within region B that are important for both transcriptional and post-transcriptional regulation.
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| 3. |
- Do, J., et al.
(författare)
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L and S bands spectrum survey in the San Francisco Bay area
- 2004
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Ingår i: PLANS 2004. - Piscataway, NJ : IEEE Communications Society. - 0780384164 ; , s. 566-572
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Konferensbidrag (refereegranskat)abstract
- The Global Positioning System (GPS) is a radio frequency (RF) communication system that consists of transmitters on the satellites and receivers on the ground. Because of substantial path loss, the received signal power from satellites is extremely weak and even below the thermal noise floor and as such is very sensitive to changes in the underlying noise floor. The goal of this work is to investigate the radio spectrum environment in the GPS band along with two additional bands, the Unified-S band and 2.4 GHz Industrial Scientific and Medical (ISM) band. The spectrum survey was conducted at various locations in the San Francisco Bay area including various urban, rural areas and airports and harbors which are operational significant to GPS. The measurement data collected in this study will provide a more accurate representation of the current status and the characteristics of the spectrum environment. Geographical variation within the sites will reveal correlation between the spectrum environment and the level of urbanization and also a comparative study on the frequency bands under different level of regulations can be used to investigate the effectiveness of the current spectrum policy
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| 4. |
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| 5. |
- Gilthorpe, Jonathan, et al.
(författare)
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Spatially specific expression of Hoxb4 is dependent on the ubiquitous transcription factor NFY.
- 2002
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Ingår i: Development. - 0950-1991 .- 1477-9129. ; 129:16, s. 3887-99
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Tidskriftsartikel (refereegranskat)abstract
- Understanding how boundaries and domains of Hox gene expression are determined is critical to elucidating the means by which the embryo is patterned along the anteroposterior axis. We have performed a detailed analysis of the mouse Hoxb4 intron enhancer to identify upstream transcriptional regulators. In the context of an heterologous promoter, this enhancer can establish the appropriate anterior boundary of mesodermal expression but is unable to maintain it, showing that a specific interaction with its own promoter is important for maintenance. Enhancer function depends on a motif that contains overlapping binding sites for the transcription factors NFY and YY1. Specific mutations that either abolish or reduce NFY binding show that it is crucial for enhancer activity. The NFY/YY1 motif is reiterated in the Hoxb4 promoter and is known to be required for its activity. As these two factors are able to mediate opposing transcriptional effects by reorganizing the local chromatin environment, the relative levels of NFY and YY1 binding could represent a mechanism for balancing activation and repression of Hoxb4 through the same site.
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| 6. |
- Ilmonen, P, et al.
(författare)
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Stress, immunocompetence and leukocyte profiles of pied flycatchers in relation to brood size manipulation
- 2003
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 136:1, s. 148-154
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Tidskriftsartikel (refereegranskat)abstract
- The two main trade-offs considered determining reproductive patterns in iteroparous organisms are the one between current and future reproduction, and the one between the number and quality of offspring. Recently, it has been suggested that these trade-offs may be mediated by stress-induced reduction in immunocompetence. To test the hypothesis that stress reduces immune function, we investigated the effects of brood size manipulation on stress hormone levels, leukocyte profiles and immune responses against challenge with novel antigens in nestling and parent male pied flycatchers (Ficedula hypoleuca). In male parents, heterophil (H) and lymphocyte (L) numbers, as well as H/L ratio increased with experimentally enlarged brood size, and corticosterone levels tended to do so, indicating that high parental work load altered their stress level and physiological state. Despite this, we found no effects on humoral immune responsiveness, measured as antibody production against diphtheria-tetanus vaccine. In nestlings, heterophil numbers and H/L ratio increased in enlarged broods, whereas T-cell-mediated immune responsiveness, measured against phytohemagglutinin (PHA), decreased in enlarged broods. The results support the view that growth-stress-induced immunosuppression may be an important physiological pathway mediating the trade-off between the number and viability of offspring. The difference in the observed immune-related responses between nestlings and males may be because we measured different aspects of the immune system (cellular vs humoral). However, it may also be a result of males lowering their own costs by feeding less, (and their mate possibly compensate by feeding more), whereas nestlings cannot escape the costs of increased intra-brood competition.
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| 7. |
- Kokkolaras, Michael, et al.
(författare)
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Mixed Variable Optimization of the Number and Composition of Heat Intercepts in a Thermal Insulation System
- 2001
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Ingår i: Optimization and Engineering. - 1389-4420 .- 1573-2924. ; 2:1, s. 42519-
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Tidskriftsartikel (refereegranskat)abstract
- In the literature, thermal insulation systems with a fixed number of heat intercepts have been optimized with respect to intercept locations and temperatures. The number of intercepts and the types of insulators that surround them were chosen by parametric studies. This was because the optimization methods used could not treat such categorical variables. Discrete optimization variables are categorical if the objective function or the constraints can not be evaluated unless the variables take one of a prescribed enumerable set of values. The key issue is that categorical variables can not be treated as ordinary discrete variables are treated by relaxing them to continuous variables with a side constraint that they be discrete at the solution. A new mixed variable programming (MVP) algorithm makes it possible to optimize directly with respect to mixtures of discrete, continuous, and categorical decision variables. The result of applying MVP is shown here to give a 65% reduction in the objective function over the previously published result for a thermal insulation model from the engineering literature. This reduction is largely because MVP optimizes simultaneously with respect to the number of heat intercepts and the choices from a list of insulator types as well as intercept locations and temperatures. The main purpose of this paper is to show that the mixed variable optimization algorithm can be applied effectively to a broad class of optimization problems in engineering that could not be easily solved with earlier methods
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| 8. |
- Lindbeck, Assar, et al.
(författare)
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The Firm as a Pool of Factor Complementarities
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a new approach to the theory of the firm by identifying factor complementarities as central to the determination of the firm’s boundaries. The factor complementarities may take a variety of forms: technological and informational complementarities, as well as economies of scale and scope. We examine the tradeoff between the gains from these complementarities and transactions costs. In so doing, we must abandon the standard dichotomy between the determinants of plant size and firm size. The influence of factor complementarities on firm size is examined in partial and general equilibrium frameworks.
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| 9. |
- Novotny, Marian, et al.
(författare)
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Evaluation of protein fold comparison servers.
- 2004
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Ingår i: Proteins. - 1097-0134. ; 54:2, s. 260-70
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Tidskriftsartikel (refereegranskat)abstract
- When a new protein structure has been determined, comparison with the database of known structures enables classification of its fold as new or belonging to a known class of proteins. This in turn may provide clues about the function of the protein. A large number of fold comparison programs have been developed, but they have never been subjected to a comprehensive and critical comparative analysis. Here we describe an evaluation of 11 publicly available, Web-based servers for automatic fold comparison. Both their functionality (e.g., user interface, presentation, and annotation of results) and their performance (i.e., how well established structural similarities are recognized) were assessed. The servers were subjected to a battery of performance tests covering a broad spectrum of folds as well as special cases, such as multidomain proteins, Calpha-only models, new folds, and NMR-based models. The CATH structural classification system was used as a reference. These tests revealed the strong and weak sides of each server. On the whole, CE, DALI, MATRAS, and VAST showed the best performance, but none of the servers achieved a 100% success rate. Where no structurally similar proteins are found by any individual server, it is recommended to try one or two other servers before any conclusions concerning the novelty of a fold are put on paper.
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| 10. |
- Olsson, Jan-Ola, et al.
(författare)
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Compression Ratio Influence on Maximum Load of a Natural Gas Fueled HCCI Engine
- 2002
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Ingår i: SAE Transactions, Journal of Engines. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 111:3, s. 442-458
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the compression ratio influence on maximum load of a Natural Gas HCCI engine. A modified Volvo TD100 truck engine is controlled in a closed-loop fashion by enriching the Natural Gas mixture with Hydrogen. The first section of the paper illustrates and discusses the potential of using hydrogen enrichment of natural gas to control combustion timing. Cylinder pressure is used as the feedback and the 50 percent burn angle is the controlled parameter. Full-cycle simulation is compared to some of the experimental data and then used to enhance some of the experimental observations dealing with ignition timing, thermal boundary conditions, emissions and how they affect engine stability and performance. High load issues common to HCCI are discussed in light of the inherent performance and emissions tradeoff and the disappearance of feasible operating space at high engine loads. The problems of tighter limits for combustion timing, unstable operational points and physical constraints at high loads are discussed and illustrated by experimental results. Finally, the influence on operational limits, i.e., emissions peak pressure rise and peak cylinder pressure, from compression ratio at high load are discussed.
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