180 research outputs found
A. Polacek. Systeme und Strukturen
No full textArmogathe Jean-Robert. A. Polacek. Systeme und Strukturen. In: Revue de l'histoire des religions, tome 194, n°2, 1978. p. 199
Quasi-Polynomial Local Search for Restricted Max-Min Fair Allocation
No full textThe restricted max-min fair allocation problem (also known as the restricted Santa Claus problem) is one of few problems that enjoys the intriguing status of having a better estimation algorithm than approximation algorithm. Indeed, Asadpour et al. [1] proved that a certain configuration LP can be used to estimate the optimal value within a factor 1/(4+ε), for any ε>0, but at the same time it is not known how to efficiently find a solution with a comparable performance guarantee. A natural question that arises from their work is if the difference between these guarantees is inherent or because of a lack of suitable techniques. We address this problem by giving a quasi-polynomial approximation algorithm with the mentioned performance guarantee. More specifically, we modify the local search of [1] and provide a novel analysis that lets us significantly improve the bound on its running time: from 2O(n) to nO(logn). Our techniques also have the interesting property that although we use the rather complex configuration LP in the analysis, we never actually solve it and therefore the resulting algorithm is purely combinatorial.QC 20130114</p
Improved dynamic cutting force model with complex coefficients at orthogonal turning
No full textSelf-excited vibration (chatter) is determined by the relation between the vibrating system and the cutting process. In current theories, the dynamic cutting force model in a form suggested by Tlusty and Polacek in the 1950s is still used. However, this model oversimplifies the dynamic cutting process by trying to express all processes using a single cutting force coefficient. Measurement results presented in this article clearly show that such simplification of the cutting process is unacceptable. This work follows upon the original measurement method by Tlusty and Polacek using controlled tool vibration. The method was intended to research the cutting process dynamics. However, the original Tlusty and Polacek method ignored the impact of the length of the workpiece surface wave. The original method is innovatively developed by taking into account the impact of the chatter frequency. The new method allows to better understand the processes occurring during dynamic cutting. As opposed to the original method, current advanced measurement equipment allows for more precise examination of the cutting process in dependence on the chatter frequency. The article shows that results obtained by the new method can be utilized for modeling the cutting force with greater precision in order to better predict the cutting process stability
A ribosome-bound tRNA half stimulates mitochondrial translation during stress recovery in Trypanosoma brucei
No full textThe protozoan parasite Trypanosoma brucei and its disease-causing relatives are among the few organisms that barely regulate the transcription of protein-coding genes. Yet, alterations in its gene expression are essential to survive in different host environments. Recently, tRNA-derived RNAs have been implicated as regulators of many cellular processes within and beyond translation. Previously, we identified the tRNAThr-3'-half (AGU) as a ribosome-associated non-coding RNA able to enhance global translation. Here we report that the tRNAThr-3'-half is generated upon starvation inside the mitochondria. The tRNAThr-3'-half associates with mitochondrial ribosomes and stimulates translation during stress recovery, positively affecting mitochondrial activity and, consequently, cellular energy production capacity. Our results describe an organelle ribosome-associated ncRNA involved in translation regulation to boost the central hub of energy metabolism as an immediate stress recovery response
Small but Powerful: The Human Vault RNAs as Multifaceted Modulators of Pro-Survival Characteristics and Tumorigenesis
No full textThe importance of non-coding RNAs for regulating gene expression has been uncovered in model systems spanning all three domains of life. More recently, their involvement in modulating signal transduction, cell proliferation, tumorigenesis and cancer progression has also made them promising tools and targets for oncotherapy. Recent studies revealed a class of highly conserved small ncRNAs, namely vault RNAs, as regulators of several cellular homeostasis mechanisms. The human genome encodes four vault RNA paralogs that share significant sequence and structural similarities, yet they seem to possess distinct roles in mammalian cells. The alteration of vault RNA expression levels has frequently been observed in cancer tissues, thus hinting at a putative role in orchestrating pro-survival characteristics. Over the last decade, significant advances have been achieved in clarifying the relationship between vault RNA and cellular mechanisms involved in cancer development. It became increasingly clear that vault RNAs are involved in controlling apoptosis, lysosome biogenesis and function, as well as autophagy in several malignant cell lines, most likely by modulating signaling pathways (e.g., the pro-survival MAPK cascade). In this review, we discuss the identified and known functions of the human vault RNAs in the context of cell proliferation, tumorigenesis and chemotherapy resistance
Transcriptome-Wide Analysis of Stationary Phase Small ncRNAs in E. coli
No full textAlmost two-thirds of the microbiome’s biomass has been predicted to be in a non-proliferating, and thus dormant, growth state. It is assumed that dormancy goes hand in hand with global downregulation of gene expression. However, it remains largely unknown how bacteria manage to establish this resting phenotype at the molecular level. Recently small non-protein-coding RNAs (sRNAs or ncRNAs) have been suggested to be involved in establishing the non-proliferating state in bacteria. Here, we have deep sequenced the small transcriptome of Escherichia coli in the exponential and stationary phases and analyzed the resulting reads by a novel biocomputational pipeline STARPA (Stable RNA Processing Product Analyzer). Our analysis reveals over 12,000 small transcripts enriched during both growth stages. Differential expression analysis reveals distinct sRNAs enriched in the stationary phase that originate from various genomic regions, including transfer RNA (tRNA) fragments. Furthermore, expression profiling by Northern blot and RT-qPCR analyses confirms the growth phase-dependent expression of several enriched sRNAs. Our study adds to the existing repertoire of bacterial sRNAs and suggests a role for some of these small molecules in establishing and maintaining stationary phase as well as the bacterial stress response. Functional characterization of these detected sRNAs has the potential of unraveling novel regulatory networks central for stationary phase biology
Ribosome-Associated ncRNAs (rancRNAs) Adjust Translation and Shape Proteomes
No full textThe regulation of protein synthesis is of extreme importance for cell survival in challenging environmental conditions. Modulating gene expression at the level of translation allows a
swift and low‐energy‐cost response to external stimuli. In the last decade, an emerging class of
regulatory ncRNAs, namely ribosome‐associated non‐coding RNAs (rancRNAs), has been discovered.
These rancRNAs have proven to be efficient players in the regulation of translation as a first
wave of stress adaptation by directly targeting the ribosome, the central enzyme of protein production. This underlying principle appears to be highly conserved, since rancRNAs are present in
all three domains of life. Here, we review the major findings and mechanistic peculiarities of
rancRNAs, a class of transcripts that is providing new and broader perspectives on the complexity
of the ribosome and translation regulation
tRNA Synthetases Are Recruited to Yeast Ribosomes by rRNA Expansion Segment 7L but Do Not Require Association for Functionality
No full textProtein biosynthesis is essential for any organism, yet how this process is regulated is not fully understood at the molecular level. During evolution, ribosomal RNA expanded in specific regions, referred to as rRNA expansion segments (ES). First functional roles of these expansions have only recently been discovered. Here we address the role of ES7La located in the large ribosomal subunit for factor recruitment to the yeast ribosome and the potential consequences for translation. Truncation of ES7La has only minor effects on ribosome biogenesis, translation efficiency and cell doubling. Using yeast rRNA deletion strains coupled with ribosome-specific mass spectrometry we analyzed the interactome of ribosomes lacking ES7La. Three aminoacyl-tRNA synthetases showed reduced ribosome association. Synthetase activities however remained unaltered suggesting that the pool of aminoacylated tRNAs is unaffected by the ES deletion. These results demonstrated that aminoacylation activities of tRNA synthetases per se do not rely on ribosome association. These findings suggest a role of ribosome-associated aminoacyl-tRNA synthetase beyond their core enzymatic functions
Mott Children's Health Center Eatfit Summer Camp II
No full textThe purpose of this study was to design an evaulation tool for EatFit Summer Camp II held at Mott Children's Health Center. This camp is in need of a formal evaluation tool to be utilized by participants thirteen to sixteen years of age. The variables that will be concentrated on are self-efficacy and environment. The final MCHC questionnaire is comprised from questions from three existing evaluation tools. Two of the tools were utilized by children/adolescents. The other questionnaire was utilized by adults; however, questions regarding environment are relevant to population being serviced.Master'sSchool of Health Professions and Studies: Health EducationUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/117736/1/Polacek.pd
Food Insecurity and Diabetes Self-Management among Youth and Young Adults with Type 1 Diabetes
No full textThesis (Master's)--University of Washington, 2018Background: Household food insecurity (FI) is associated with measures of diabetes self-management among older adults with diabetes. To our knowledge, there is no existing literature assessing this association among youth and young adults (YYA) with type 1 diabetes (T1D). Objective: To examine the association between FI and diabetes self-management, as measured by frequency of blood glucose monitoring and missed diabetes medication, among YYA with T1D. Methods: This is a cross-sectional study using data collected from 210 participants with T1D in South Carolina and Washington through the SEARCH for Diabetes in Youth study. FI was measured using the Household Food Security Survey Module and was scored 0-10 based on a continuous linear scale. Diabetes self-management was determined using two variables, frequency of glucose monitoring and missed medications, which were measured via health questionnaires. Results: We found that FI is significantly associated with frequency of missed diabetes medications, but not frequency of blood glucose monitoring. A one-unit increase in the standardized FI score was associated with a 24% increase in the odds of missing diabetes medication at least once per month (OR=1.24, 95% CI 1.02, 1.50, p=0.027). Socioeconomic status was significantly associated with frequency of blood glucose monitoring (OR=2.39, 95% CI 1.25, 4.56, p=0.008). Conclusion: These results suggest that FI is negatively associated with diabetes self-management as demonstrated by an increase in missed diabetes medication. Future studies are necessary to illuminate the relationship between FI and other self-management behaviors and examine the mechanisms through which FI may impact self-management
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