Modules of covariants in modular invariant theory

Let the finite group $G$ act linearly on the vector space $V$ over the field $k$ of arbitrary characteristic. If $H<G$ is a subgroup the extension of invariant rings $k[V]^G\subset k[V]^H$ is studied using modules of covariants. An example of our results is the following. Let $W$ be the subgroup of $G$ generated by the reflections in $G$. A classical theorem due to Serre says that if $k[V]$ is a free $k[V]^G$-module then $G=W$. We generalize this result as follows. If $k[V]^H$ is a free $k[V]^G$-module then $G$ is generated by $H$ and $W$, and the invariant ring $k[V]^{H\cap W}$ is free over $k[V]^W$ and generated as an algebra by $H$-invariants and $W$-invariants.Comment: 36 pages, proofs of main theorems have been improve

Correlating Cell Behavior with Tissue Topology in Embryonic Epithelia

Measurements on embryonic epithelial tissues in a diverse range of organisms have shown that the statistics of cell neighbor numbers are universal in tissues where cell proliferation is the primary cell activity. Highly simplified non-spatial models of proliferation are claimed to accurately reproduce these statistics. Using a systematic critical analysis, we show that non-spatial models are not capable of robustly describing the universal statistics observed in proliferating epithelia, indicating strong spatial correlations between cells. Furthermore we show that spatial simulations using the Subcellular Element Model are able to robustly reproduce the universal histogram. In addition these simulations are able to unify ostensibly divergent experimental data in the literature. We also analyze cell neighbor statistics in early stages of chick embryo development in which cell behaviors other than proliferation are important. We find from experimental observation that cell neighbor statistics in the primitive streak region, where cell motility and ingression are also important, show a much broader distribution. A non-spatial Markov process model provides excellent agreement with this broader histogram indicating that cells in the primitive streak may have significantly weaker spatial correlations. These findings show that cell neighbor statistics provide a potentially useful signature of collective cell behavior.Comment: PLoS one 201

A framework for balancing information collection and data transmission

Network protocol performance is closely related to knowledge about the network state. However, acquiring such knowledge expends network bandwidth resource. Thus a trade off exists between the amount of bandwidth resource expended in acquiring knowledge about network state, and the improved protocol performance due to such knowledge. Previous work used rate distortion theory to calculate the minimum information required for certain network performance. However, this limit is asymptotic and might not be achievable due to the introduced infinite delay. This work develops a non-asymptotic framework to find a practical bound of the required information for certain network performance, and the strategies for implementing network information collection. The framework is illustrated by a wireless scheduling problem to show the quantitative relationship between collected traffic information and network throughput. Furthermore, we calculate the effective data rate by considering the overhead of network information collection, and determine the optimal resource allocation between information collection and data transmission.published_or_final_versio

The temporal value of information to network protocols: an analytical framework

Network protocol performance is closely related to the available information about the network state. However, acquiring such information expends network bandwidth resource. Thus a trade-off exists between the amount of information collected about the network state, and the improved protocol performance due to this information. A framework has been developed to study the optimal trade-off between the amount of collected information and network performance. However, the effect of information delay is not considered. In this paper, we extend the framework to study the impact of information delay on the value of network state information to network protocols, based on which optimal periodic information update policies could be obtained. The framework is illustrated by an example of multiuser scheduling, and observations about the impact of information delay on network protocols are obtained. © 2015 IEEE.postprin

The Use of English Language in Tourism Workplaces in Pakmeng Beach Area, Trang Province

  This research was conducted (1) to explore English language skills used by front desk staff in tourism workplaces in Pakmeng beach, Trang province, Thailand (2) to identify the frequency of English languages skills used by the front office staff in tourism workplaces and (3) to investigate the interests and needs in improving English language skills by front office staff. By purposive sampling, the samples consisted of 40 front office staff of hotels, resorts and the tourism agencies in Pakmeng beach, Trang province. The questionnaire was collected and analyzed by descriptive statistics using percentage, frequency, Means and Standard deviation. The major findings revealed that listening was the most common skill used by employees, followed by speaking, reading and writing skill. English listening skills such as listening to customers’ questions and giving information about hotels/tour services were frequently used by the employees in the tourism workplaces. The most three common interests and needs to improve English language were vocabulary relating to hospitality and tourism, followed by giving information about hotel services and tour services and giving information about tourist attractions.   The findings from semi- structured interviews showed that most of the employees considered that the English language was a vital part of their job and had become a core criteria for their career in tourism workplaces, especially listening and speaking skills. Therefore, they wanted to improve their English speaking and listening skills with respect to accommodation booking , tourist attraction information , price quotation and  general conversation.

Excess caffeine exposure impairs eye development during chick embryogenesis

Caffeine has been an integral component of our diet and medicines for centuries. It is now known that over consumption of caffeine has detrimental effects on our health, and also disrupts normal foetal development in pregnant mothers. In this study, we investigated the potential teratogenic effect of caffeine over-exposure on eye development in the early chick embryo. Firstly, we demonstrated that caffeine exposure caused chick embryos to develop asymmetrical microphthalmia and induced the orbital bone to develop abnormally. Secondly, caffeine exposure perturbed Pax6 expression in the retina of the developing eye. In addition, it perturbed the migration of HNK-1(+) cranial neural crest cells. Pax6 is an important gene that regulates eye development, so altering the expression of this gene might be the cause for the abnormal eye development. Thirdly, we found that reactive oxygen species (ROS) production was significantly increased in eye tissues following caffeine treatment, and that the addition of anti-oxidant vitamin C could rescue the eyes from developing abnormally in the presence of caffeine. This suggests that excess ROS induced by caffeine is one of the mechanisms involved in the teratogenic alterations observed in the eye during embryogenesis. In sum, our experiments in the chick embryo demonstrated that caffeine is a potential teratogen. It causes asymmetrical microphthalmia to develop by increasing ROS production and perturbs Pax6 expression