Data Dissemination Performance in Large-Scale Sensor Networks

As the use of wireless sensor networks increases, the need for (energy-)efficient and reliable broadcasting algorithms grows. Ideally, a broadcasting algorithm should have the ability to quickly disseminate data, while keeping the number of transmissions low. In this paper we develop a model describing the message count in large-scale wireless sensor networks. We focus our attention on the popular Trickle algorithm, which has been proposed as a suitable communication protocol for code maintenance and propagation in wireless sensor networks. Besides providing a mathematical analysis of the algorithm, we propose a generalized version of Trickle, with an additional parameter defining the length of a listen-only period. This generalization proves to be useful for optimizing the design and usage of the algorithm. For single-cell networks we show how the message count increases with the size of the network and how this depends on the Trickle parameters. Furthermore, we derive distributions of inter-broadcasting times and investigate their asymptotic behavior. Our results prove conjectures made in the literature concerning the effect of a listen-only period. Additionally, we develop an approximation for the expected number of transmissions in multi-cell networks. All results are validated by simulations

Queues with random back-offs

We consider a broad class of queueing models with random state-dependent vacation periods, which arise in the analysis of queue-based back-off algorithms in wireless random-access networks. In contrast to conventional models, the vacation periods may be initiated after each service completion, and can be randomly terminated with certain probabilities that depend on the queue length. We examine the scaled queue length and delay in a heavy-traffic regime, and demonstrate a sharp trichotomy, depending on how the activation rate and vacation probability behave as function of the queue length. In particular, the effect of the vacation periods may either (i) completely vanish in heavy-traffic conditions, (ii) contribute an additional term to the queue lengths and delays of similar magnitude, or even (iii) give rise to an order-of-magnitude increase. The heavy-traffic asymptotics are obtained by combining stochastic lower and upper bounds with exact results for some specific cases. The heavy-traffic trichotomy provides valuable insight in the impact of the back-off algorithms on the delay performance in wireless random-access networks

NMR Dynamics Investigation of Ligand-Induced Changes of Main and Side-Chain Arginine N-H’s in Human Phosphomevalonate Kinase

Phosphomevalonate kinase (PMK) catalyzes phosphoryl transfer from adenosine triphosphate (ATP) to mevalonate 5-phosphate (M5P) on the pathway for synthesizing cholesterol and other isoprenoids. To permit this reaction, its substrates must be brought proximal, which would result in a significant and repulsive buildup of negative charge. To facilitate this difficult task, PMK contains 17 arginines and eight lysines. However, the way in which this charge neutralization and binding is achieved, from a structural and dynamics perspective, is not known. More broadly, the role of arginine side-chain dynamics in binding of charged substrates has not been experimentally defined for any protein to date. Herein we report a characterization of changes to the dynamical state of the arginine side chains in PMK due to binding of its highly charged substrates, ATP and M5P. These studies were facilitated by the use of arginine-selective labeling to eliminate spectral overlap. Model-free analysis indicated that while substrate binding has little effect on the arginine backbone dynamics, binding of either substrate leads to significant rigidification of the arginine side chains throughout the protein, even those that are \u3e8 Å from the binding site. Such a global rigidification of arginine side chains is unprecedented and suggests that there are long-range electrostatic interactions of sufficient strength to restrict the motion of arginine side chains on the picosecond-to-nanosecond time scale. It will be interesting to see whether such effects are general for arginine residues in proteins that bind highly charged substrates, once additional studies of arginine side-chain dynamics are reported

Substrate Induced Structural and Dynamics Changes in Human Phosphomevalonate Iinase and Implications for Mechanism

Phosphomevalonate kinase (PMK) catalyzes an essential step in the mevalonate pathway, which is the only pathway for synthesis of isoprenoids and steroids in humans. PMK catalyzes transfer of the γ-phosphate of ATP to mevalonate 5-phosphate (M5P) to form mevalonate 5-diphosphate. Bringing these phosphate groups in proximity to react is especially challenging, given the high negative charge density on the four phosphate groups in the active site. As such, conformational and dynamics changes needed to form the Michaelis complex are of mechanistic interest. Herein, we report the characterization of substrate induced changes (Mg-ADP, M5P, and the ternary complex) in PMK using NMR-based dynamics and chemical shift perturbation measurements. Mg-ADP and M5P Kd\u27s were 6–60 μM in all complexes, consistent with there being little binding synergy. Binding of M5P causes the PMK structure to compress (τc = 13.5 nsec), whereas subsequent binding of Mg-ADP opens the structure up (τc = 15.6 nsec). The overall complex seems to stay very rigid on the psec-nsec timescale with an average NMR order parameter of S2 ∼0.88. Data are consistent with addition of M5P causing movement around a hinge region to permit domain closure, which would bring the M5P domain close to ATP to permit catalysis. Dynamics data identify potential hinge residues as H55 and R93, based on their low order parameters and their location in extended regions that connect the M5P and ATP domains in the PMK homology model. Likewise, D163 may be a hinge residue for the lid region that is homologous to the adenylate kinase lid, covering the “Walker-A” catalytic loop. Binding of ATP or ADP appears to cause similar conformational changes; however, these observations do not indicate an obvious role for γ-phosphate binding interactions. Indeed, the role of γ-phosphate interactions may be more subtle than suggested by ATP/ADP comparisons, because the conservative O to NH substitution in the β-γ bridge of ATP causes a dramatic decrease in affinity and induces few chemical shift perturbations. In terms of positioning of catalytic residues, binding of M5P induces a rigidification of Gly21 (adjacent to the catalytically important Lys22), although exchange broadening in the ternary complex suggests some motion on a slower timescale does still occur. Finally, the first nine residues of the N-terminus are highly disordered, suggesting that they may be part of a cleavable signal or regulatory peptide sequence. Proteins 2009. © 2008 Wiley-Liss, Inc

Molecular Docking and NMR Binding Studies to Identify Novel Inhibitors of Human Phosphomevalonate Kinase

Phosphomevalonate kinase (PMK) phosphorylates mevalonate-5-phosphate (M5P) in the mevalonate pathway, which is the sole source of isoprenoids and steroids in humans. We have identified new PMK inhibitors with virtual screening, using autodock. Promising hits were verified and their affinity measured using NMR-based 1H–15N heteronuclear single quantum coherence (HSQC) chemical shift perturbation and fluorescence titrations. Chemical shift changes were monitored, plotted, and fitted to obtain dissociation constants (Kd). Tight binding compounds with Kd’s ranging from 6–60 μM were identified. These compounds tended to have significant polarity and negative charge, similar to the natural substrates (M5P and ATP). HSQC cross peak changes suggest that binding induces a global conformational change, such as domain closure. Compounds identified in this study serve as chemical genetic probes of human PMK, to explore pharmacology of the mevalonate pathway, as well as starting points for further drug development

Pengaruh Independensi, Kompetensi, Pengalaman Kerja, Pendidikan, Perbedaan Gender, dan Integritas Auditor terhadap Profesionalisme Auditor Bpk RI Perwakilan Provinsi Jambi

This study aimed to examine the effect of the influence of independency, competency, work experience, education, gender difference, and auditors integrity to professionalism of BPK RI\u27s auditors especially those who are working in auditing firm representative Jambi province. Professional auditor is the auditor who acknowledges its responsibility towards society, the responsibility of the client, the responsibility towards colleagues included to behave respectable, though this is a personal sacrifice. Methods of data collection in this study is a method of questionnaire instruments that are delivered directly to the auditing firm representative Jambi province though the people work who work in community relations. Population in this study is BPK RI\u27s auditors who worked in a auditing firm representative Jambi province. The entire population to be sampled by the researches. The number of samples used in this study were 33 people who worked in auditing firm representative Jambi province. Methods of analysis is conducted with a multiple regression analysis version 20,00 for windows. The results for testing that has been done. Practical regression F ( F Test ) showed that the auditor\u27s competency, education, and integrity had a influences toward auditor professionalism. Analysis using the coefficient of determination ( R2 ) found that the contribution of the influence of the independent variable on the dependent variable is 81,3 % while the remaining 18,7% is influenced by other variables not included in this study

Pengaruh Kualitas Produk, Harga, dan Kualitas Pelayanan terhadap Kepuasan Pengguna Cafe dan Resto Cabana Manado

Persaingan yang semakin ketat menuntut para pelaku bisnis untuk memaksimalkan kinerjanya melalui kualitas produk, harga, dan kualitas pelayanan untuk dapat bertahan dalam persaingan bisnis dan mampu menciptakan kepuasan pelanggan. Tujuan penelitian ini adalah untuk mengetahui pengaruh kualitas produk, harga, dan kualitas pelayanan terhadap kepuasan pengguna Cafe dan Resto Cabana Manado. Jenis penelitian yang digunakan adalah penelitian asosiatif dan tekhnik analisis menggunakan regresi linear berganda. Hasil penelitian menunjukan bahwa kualitas produk, harga dan kualitas pelayanan berpengaruh positif terhadap kepuasan pengguna Cafe dan Resto Cabana Manado. Kualitas produk berpengaruh namun tidak signifikan terhadap kepuasan pengguna. Harga dan kualitas pelayanan berpengaruh signifikan terhadap kepuasan pengguna. Manajemen Cafe dan Resto Cabana Manado sebaiknya meningkatkan kualitas produk agar kepuasaan pengguna dapat selalu terpenuhi