Home About us Contact
|
Home About us Contact | ||
|
|
||
Stringent Requirements (stringent + requirement)
Selected AbstractsA modified CRISIS-HSQC for band-selective IMPRESSMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2005Scott A. Bradley Abstract CRISIS (Compensation of Refocusing Inefficiency with Synchronized Inversion Sweep) is a powerful technique for obtaining multiplicity-edited HSQC spectra without compromising sensitivity. However, the stringent requirement for the duration of the CRISIS waveforms makes them unsuitable for other functions, such as band selection or IMPRESS (IMProved REsolution using Symmetrically Shifted pulses). We report here a modified CRISIS-gHSQC pulse sequence employing time-reversed 13C ,/2 EBURP-2 pulses. This IC-bs-gHSQC (IMPRESS-CRISIS-bs-gHSQC) sequence was found to be equally useful for acquiring multiplicity-edited, band-selective spectra individually or in tandem with IMPRESS. Remarkably, the latter provides multiple spectra in significantly less time and is the preferred approach when several crowded regions need to be assigned unambiguously. The use of adiabatic sweeps and the CRISIS pulses enable IC-bs-gHSQC to give better sensitivity than the original IMPRESS sequence for band-selective spectra. Copyright © 2005 John Wiley & Sons, Ltd. [source] Chiral molecules with polyhedral T, O, or I symmetry: Theoretical solution to a difficult problem in stereochemistryCHIRALITY, Issue 8 2008Sri Kamesh Narasimhan Abstract Ever since point groups of symmetry have been used to describe molecules after Van't Hoff and Le Bel proposed tetrahedral structures for carbon atoms in 1874, it remains difficult to design chiral molecules with polyhedral symmetry T, O, or I. Past theoretical and experimental studies have mainly accomplished molecular structures that have the conformations for satisfying the T symmetry. In this work, we present a general theoretical approach to construct rigid molecular structures that have permanently the symmetry of T, O, and I. This approach involves desymmetrizaton of the vertices or the edges of Platonic solid-shaped molecules with dissymmetric moieties. Using density functional theory (DFT) and assisted model building and energy refinement (AMBER) computational methods, the structure, the rigidity, and the symmetry of the molecule are confirmed by assessing the lowest energy conformation of the molecule, which is initially presented in a planar graph. This method successfully builds molecular structures that have the symmetry of T, O, and I. Interestingly, desymmetrization of the edges has a more stringent requirement of rigidity than desymmetrization of the vertices for affording the T, O, or I symmetry. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] Electrochemistry at High Pressures: A ReviewELECTROANALYSIS, Issue 10 2004Debora Giovanelli Abstract High pressure electrochemical studies are potentially dangerous and less immediately implemented than conventional investigations. Technical obstacles related to properties of the working electrode material, preparation of its surface, availability of suitable reference electrodes, and the need for specially designed high pressure equipment and cells may account for the relative lack of experimental data on electrochemistry at high pressures. However, despite the stringent requirements for system and equipment stability, significant developments have been made in recent years and the combination of electrochemical methods with high hydrostatic pressure has provided useful insights into the thermodynamics, kinetics, and other physico-chemical characteristics of a wide range of redox reactions. In addition to fundamental information, high pressure electrochemistry has also lead to a better understanding of a variety of processes under non-classical conditions with potential applications in today's industrial environment from extraction and electrosynthesis in supercritical fluids to measurement of the pH at the bottom of the ocean. The purpose of this article is to detail the experimental pressurizing apparatus for electroanalytical measurements at high pressures and to review the relevant literature on the effect of pressure on electrode processes and on the properties of aqueous electrolyte solutions. [source] Regulation of Injected Ground Water TracersGROUND WATER, Issue 4 2000Skelly A. Holmbeck-Pelham Ground water tracer tests are routinely performed to estimate aquifer flow and transport properties, including the determination of well capture zones, hydrogeologic parameters, and contaminant travel times. Investigators may be unaware of tracer test reporting requirements and may fail to notify their regulatory agency prior to conducting tracer tests. The injection of tracers falls under the jurisdiction of the federal Underground Injection Control (UIC) program, which regulates the introduction of substances into underground sources of drinking water as part of the Safe Drinking Water Act. The UIC program is administered by the U.S. Environmental Protection Agency (EPA) and by states with EPA-approved programs. The federal UIC program requires that tracer tests must not endanger underground sources of drinking water, and all tracer tests must be reported prior to injection. We contacted the UIC program administrator for every state in early 1997. Some states report having more stringent requirements, while some states do not meet minimum federal requirements. Although the primary responsibility for ground water tracer selection and use rests on the investigator, national guidance is required to assure compliance with the UIC program. To assist investigators, we present acceptable tracers that have been identified by two states, Nevada and South Carolina, that require no further regulatory review. [source] A compact dynamic channel assignment scheme based on Hopfield networks for cellular radio systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2009A. Dang Abstract In this paper, a new channel assignment strategy named compact dynamic channel assignment (CDCA) is proposed. The CDCA differs from other strategies by consistently keeping the system in the utmost optimal state, and thus the scheme allows to determine a call succeeding or failing by local information instead of that of the whole network. It employs Hopfield neural networks for optimization which avoids the complicated assessment of channel compactness and guarantees optimum solutions for every assignment. A scheme based on Hopfield neural network is considered before; however, unlike others, in this algorithm an energy function is derived in such a way that for a neuron, the more a channel is currently being allocated in other cells, the more excitation the neuron will acquire, so as to guarantee each cluster using channels as few as possible. Performance measures in terms of the blocking probability, convergence rate and convergence time are obtained to assess the viability of the proposed scheme. Results presented show that the approach significantly reduces stringent requirements of searching space and convergence time. The algorithm is simple and straightforward, hence the efficient algorithm makes the real-time implementation of channel assignment based on neural network feasibility. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance evaluation of adaptive routing algorithms in packet-switched intersatellite link networksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2002Mihael Mohor Abstract This paper addresses the performance evaluation of adaptive routing algorithms in non-geostationary packet-switched satellite communication systems. The dynamic topology of satellite networks and variable traffic load in satellite coverage areas, due to the motion of satellites in their orbit planes, pose stringent requirements to routing algorithms. We have limited the scope of our interest to routing in the intersatellite link (ISL) segment. In order to analyse the applicability of different routing algorithms used in terrestrial networks, and to evaluate the performance of new algorithms designed for satellite networks, we have built a simulation model of a satellite communication system with intersatellite links. In the paper, we present simulation results considering a network-uniform source/destination distribution model and a uniform source,destination traffic flow, thus showing the inherent routing characteristics of a selected Celestri-like LEO satellite constellation. The updates of the routing tables are centrally calculated according to the Dijkstra shortest path algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source] Offline, multidetector intensity interferometers , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Implications, applications ABSTRACT Intensity interferometry removes the stringent requirements on mechanical precision and atmospheric corrections that plague all amplitude interferometry techniques at the cost of severely limited sensitivity. A new idea we recently introduced, very high redundancy, alleviates this problem. It enables the relatively simple construction (,1 cm mechanical precision) of a ground-based astronomical facility able to transform a two-dimensional field of point-like sources to a three-dimensional distribution of microarcsec resolved systems, each imaged in several optical bands. Each system will also have its high-resolution residual timing, high-quality (inside each band) spectra and light curve, emergent flux, effective temperature, polarization effects and perhaps some thermodynamic properties, all directly measured. All the above attributes can be measured in a single observation run of such a dedicated facility. We conclude that after three decades of abandonment, optical intensity interferometry deserves another review, also as a ground-based alternative to the science goals of space interferometers. [source] The current global status of chinese materia medicaPHYTOTHERAPY RESEARCH, Issue 10 2009Liu Xinmin Abstract The Chinese government has recently established a national project to improve the standards of Chinese Materia Medica (CMM) products, particularly regarding their quality control and safety evaluation, in order to promote modernization and increase international trade. In 2006, the global sales value of Chinese medicinal products increased to 20 billion US$, and the export value of CMM was up to more than 1 billion US$. However, the standard of these products still needs to be improved to meet the more stringent requirements of the international markets. Over the past decade we have witnessed the increasing growth in popularity of health foods and herbal medicinal products, especially Chinese Materia Medica products (CMM). Copyright © 2009 John Wiley & Sons, Ltd. [source] A privacy challenge to longitudinal study methods: patient-derived codesAUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 4 2006Fiona J. Clay Recent changes to privacy legislation in Australia have resulted in more stringent requirements with respect to maintaining the confdentiality of patient health information. We describe a method employed to de-identify health information collected in a longitudinal study using codes. Using a patient-derived code that did not change during the life of the study follow-up resulted in errors in a quarter of the follow-up surveys. This may introduce bias that could compromise the validity of the study. Alternative methods of coding may alleviate some of these issues. However, removal of some of the constraints imposed by interpretations of privacy legislation may be the best way forward. [source] RADIOSTAR: Providing wireless coverage over Gigabit EthernetBELL LABS TECHNICAL JOURNAL, Issue 1 2009Zhengxiang Ma RadioStar is a novel system developed by Bell Labs to provide low cost, cellular wireless coverage primarily targeted for enterprises, public spaces, and residences. The underlying concept is to digitize the output radio signals of a base station and to transport these signals over a Gigabit Ethernet network to multiple low-cost radio frequency radiation points. The received signals are returned through the network to the base station. This paper presents the architecture, implementation, and demonstration of RadioStar. It is shown how handoffs and precise frequency synchronization and timing control over a Gigabit Ethernet network can be established in such a way that the most stringent requirements of cellular communication air interfaces are satisfied. By converging cellular signal transport onto Gigabit Ethernet data networks, RadioStar can achieve substantially lower hardware and installation costs, while providing higher performance, more flexibility, and better operation, administration, and maintenance than current solutions. RadioStar concepts are being used in the ClearFill Star in-building product developed by the RFS business division of Alcatel-Lucent and currently being deployed commercially. © 2009 Alcatel-Lucent. [source] | ||||||||||||||||