bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic analysis of temperature and heat gains in classrooms with different type of windows
Authors: Krneta Radojka , Bjekic Miroslav , Peulic Aleksandar , Dragicevic Snezana
Published: July 2007

Energy consumption in buildings, in schools as well, in Serbia and Montenegro is significantly higher than is defined in world?s energy standards. Heating energy is the biggest part of total energy consumption in schools. Energy losses through the windows reach up to 40% of total energy for heating of building that points out the importance of economically usage and saving of energy. This paper presents one-week analysis of temperatures and heat gains for two classrooms with different type of windows. The analysis is performed by Design Builder software. Due to heat losses analyses continual measurements of ambient and outside temperatures with sampling time of one hour have been performed. The measurements were performed in two classrooms; in one classroom, there are old windows with wood frames, whereas in the other there are new PVC windows. The system for temperature measuring was realized based on microcontroller and a digital temperature sensor. Taking into account measured and simulation results, the relevant conclusions were performed regarding energy consumption efficiency for school buildings heating. .
Numerical investigation of fluid flow and heat transfer characteristics in sine, triangular, and arc-shaped channels
Authors: Hossain Zakir , Islam Sadrul
Published: July 2007

Time dependent Navier-Stokes and energy equations have been solved to investigate the fluid flow and heat transfer characteristics in wavy channels. Three different types of two dimensional wavy geometries (e.g. sine-shaped, triangular, and arc-shaped) are considered. All of them are of single wave and have same geometric dimensions. Periodic boundary conditions are used to attain fully developed flow. The flow in the channels has been observed to be steady up to a critical Reynolds number, which depends on the geometric configuration. Beyond the critical Reynolds number a self-sustained oscillatory flow has been observed. As a result of this oscillation, there is increased mixing between core and the near-wall fluids, thereby increasing the heat transfer rate. For the same geometric dimensions, flow becomes unsteady at relatively lower Reynolds number in the arc-shaped channel. .
Laminar fully developed mixed convection with viscous dissipation in a uniformly heated vertical double-passage channel
Authors: Salah El-Din
Published: July 2007

Fully developed laminar mixed convection has been investigated numerically in a vertical double-passage channel by taking into account the effect of viscous dissipation. The channel is divided into two passages by means of a thin, perfectly conductive plane baffle and the walls are uniformly heated. The effects of Brinkman number and the ratio between Grashof and Reynolds numbers on the velocity and temperature profiles and the Nusselt number on the hot wall have been analyzed. The results show that these effects depend mainly on the baffle position. .
Combined of magnetic field and thermophoresis particle deposition in free convection boundary layer from a vertical flat plate embedded in a porous medium
Authors: Bakier Yousof , Mansour Ahmed
Published: July 2007

Deals with heat and mass transfer by steady laminar boundary layer flow of Newtonian, viscous fluid over a vertical flat plate embedded in a fluid-saturated porous medium in the presence of thermophoretic and magnetic field. The resulting similarity equation are solved by finite difference marching technique. The nature of variation of particle concentration profile and magnetic field with respect to buoyancy force, Fw, and Prandtl number is found to be similar. Comparisons with previous published work are performed and the results are found to be in excellent agreement. .
Solar equipment for preheating bitumen
Authors: Luminosu Ioan , de Sabata , But Adrian
Published: July 2007

This paper presents results of the research and development of the process for preheating bitumen using solar energy obtained at the Polytechnic University of Timisoara. The aim of the research was examination of the opportunity to use solar energy for preheating bitumen and to optimize connection between several solar collectors. Results of the investigation were tested in real industrial conditions by organizing slow process of the solar exposure in passive regime on the roof of the building where the bitumen is stored. In present paper laboratory installation using solar energy for heating bitumen in close to real conditions is described. The experimental results indicates an efficiency about of 25-30% and the temperature level of 54-57?C. In second part of the paper the results obtained at the industrial installation for bitumen heating in large reservoir containing 30 t of material were analyzed. Paper is addressed to the specialists? aiming to extend use of solar energy in different fields of application. .
Application of upward flame spread for the prediction of SBI and ISO room corner (and parallel wall) experiments and classification
Authors: Delichatsios Michael
Published: July 2007

The flammability hazard assessment of wall and ceiling linings has occupied the attention of fire scientists and engineers and regulators over the last fifty years. Several tests (small, medium, and large) have been developed to classify the flammability of linings and predict their burning behavior in real enclosure fire situations. We examine in some detail three such efforts: (a) the development of an experimental room and a 9 ft vertical wall full scale test by Ferris leading to the Early Fire Hazard test in Australia, (b) the ISO room corner test, and (c) The new SBI (Single Burning Item test) which maybe the most thoroughly examined test in the history of flammability testing. Of these tests, the experimental room used by Ferris and the ISO room corner test may be considered as end use applications for medium size rooms whereas the SBI test and the vertical wall test by Ferris are intermediate scale test designed to represent the room fire behavior in a more controlled way. Performance criterion in the ISO room corner test is the time to reach flashover. Performance criteria in the SBI test are related to the fire growth in an open corner (no ceiling) configuration due to upward flame spread. Performance criterion in the experimental room of Ferris was the time to reach untenable conditions in the room. Finally, performance criterion in the vertical wall of Ferris was the time interval from ignition until the flames reach the top of the wall. Examination of all these efforts has led to consistently validating a new correlation of the performance criteria of these tests with small-scale cone calorimeter tests whenever both data are available. Previous correlations are also discussed. The new correlation compares well with essential features of upward flame spread as this is related to flammability properties. Comparison between the ISO room corner test and the SBI test leads to suggestions regarding the suitability of these tests as a regulatory tool. Some comments are also directed towards a new test method of parallel wall panels recently proposed by Fmglobal. This test method can be analyzed using the same methodology outlined in this paper.
Effect of char layer on transient thermal oxidative degradation of polyethylene
Authors: Esfahani Javad , Abdolabadi Ali
Published: July 2007

A transient one dimensional model has been presented to simulate degradation and gasification of polyethylene, in early stage of fire growth. In the present model effect of oxygen on degradation and rate of polymer gasification while the sample is subjected to an external radiative heat source is numerically investigated. This model includes different mechanism, which affect the degradation process, such as in depth thermal oxidative decomposition, in depth absorption of radiation, heat transfer, volatiles advection in solid phase and convective heat transfer on surface. Also effects of radiative parameters, due to formation of char layer such as surface reflectivity and absorptivity on thermal degradation of polyethylene are investigated. The results for 40 kW/m2 heat source are reported and yielded realistic results, comparing to the published experimental data. The results show that an increase in oxygen concentration leads to considerable increase in gasification rate and also leads to sharp increase of surface temperature. .
Recommendation of tests for assessing flame spread of materials in Hong Kong
Authors: Chow Wan , Leung Wai
Published: July 2007

Performance-based design for passive building fire safety provisions is accepted by the authority in Hong Kong since 1998. This is also known as the "fire engineering approach", though the performance-based fire code is not yet available. To cope with the use of new building materials, appropriate flame spread tests on materials and components should be specified. After reviewing four standard tests in the literature, i.e. ASTM E1321-97a, BS476: Part 7: 1997, ASTM E84-99/NFPA 255, and ISO 9705: 1993(E), it appears that ISO 9705: 1993(E) is suitable for assessing the flame spread of materials. .
The effect of surface regression on the downward flame spread over a solid fuel in a quiescent ambient
Authors: Ayani Mohammad , Esfahani Javad , Sousa Antonio
Published: July 2007

The present work is addressed to the numerical study of the transient laminar opposed-flow flame spread over a solid fuel in a quiescent ambient. The transient governing equations - full Navier-Stokes, energy, and species (oxygen and volatiles) for the gas phase, and continuity and energy equations for the solid phase (fuel) with primitive variables are discretized in a staggered grid by a control volume approach. The second-order Arrhenius kinetics law is used to determine the rate of consumption of volatiles due to combustion, and the zero-order Arrhenius kinetics law is used to determine the rate of degradation of solid fuel. The equations for the fluid and solid phases are solved simultaneously using a segregated technique. The physical and thermo-physical properties of the fluid (air) such as density, thermal conductivity, and viscosity vary with temperature. The surface regression of the solid fuel is modeled numerically using a discrete formulation, and the effect upon the results is analyzed. The surface regression of the solid fuel as shown affects on the fuel surface and gas temperature, mass flux and velocity of volatiles on the top surface of fuel, total energy transferred to the solid phase, etc. It seems the results to be realistic. .
Large-scale pool fires
Authors: Steinhaus Thomas , Welch Stephen , Carvel Richard , Torero José
Published: July 2007

A review of research into the burning behavior of large pool fires and fuel spill fires is presented. The features which distinguish such fires from smaller pool fires are mainly associated with the fire dynamics at low source Froude numbers and the radiative interaction with the fire source. In hydrocarbon fires, higher soot levels at increased diameters result in radiation blockage effects around the perimeter of large fire plumes; this yields lower emissive powers and a drastic reduction in the radiative loss fraction; whilst there are simplifying factors with these phenomena, arising from the fact that soot yield can saturate, there are other complications deriving from the intermittency of the behavior, with luminous regions of efficient combustion appearing randomly in the outer surface of the fire according the turbulent fluctuations in the fire plume. Knowledge of the fluid flow instabilities, which lead to the formation of large eddies, is also key to understanding the behavior of large-scale fires. Here modeling tools can be effectively exploited in order to investigate the fluid flow phenomena, including RANS- and LES-based computational fluid dynamics codes. The latter are well-suited to representation of the turbulent motions, but a number of challenges remain with their practical application. Massively-parallel computational resources are likely to be necessary in order to be able to adequately address the complex coupled phenomena to the level of detail that is necessary.
Combustion of liquid fuels floating on water
Authors: Garo Jean-Pierre , Koseki Hiroshi , Vantelon Jean-Pierre , Fernandez-Pello Carlos
Published: July 2007

The research presented consists of a study of the burning characteristics of a liquid fuel floating on water with emphasis in the phenomena known as boilover. The problem is of technical interest in the petro-chemical industry, particularly from the point of view of pollution and fires resulting from accidental liquid fuel spills in open water. Testing with multicomponent fuels gives information's about events that can occur in a practical situation, while testing with single component fuels permits obtaining fundamental information about the problem. It evidences the major effects caused by the transfer of heat from the fuel to the water underneath. One of these effects is the disruptive burning of the fuel known as boilover, that is caused by the water boiling and splashing, and results in a sharp increase in burning rate and often in the explosive burning of the fuel. It is shown that this event is caused by the onset of water boiling nucleation at the fuel/water interface and that it occurs at an approximate constant temperature that is above the saturation temperature of the water (water is superheated). These measurements conducted in two laboratories, address the major issues of the process by analyzing the effect of the variation of the parameters of the problem (initial fuel-layer thickness, pool diameter, and fuel type), on the burning rate, time to start of boilover, pre-boilover mass ratio, and boilover intensity. Finally, two types of modeling are proposed to describe the heat transfer in fuel and water phases: one simple for practical purposes, the other, more elaborated and transient, taking particularly into consideration the radiation in depth.
An inverse Stefan problem relevant to boilover: Heat balance integral solutions and analysis
Authors: Hristov Jordan
Published: July 2007

Stefan problems relevant to burning oil-water systems are formulated. Two moving boundary sub-problems are defined: burning liquid surface and formation of a distillation ("hot zone") layer beneath it. The basic model considers a heat transfer equation with internal neat generation due to radiation flux absorbed in the fuel depth. Inverse Stefan problem corresponding to the first case solved by the heat balance integral method and dimensionless scaling of semi-analytical solutions are at issue. .
Comparison of calculation methods for smoke and heat evacuation for enclosure fires in large compartments
Authors: Merci Bart , Vandevelde Paul
Published: July 2007

A comparative study is presented of different calculation methods with respect to the evacuation of smoke and heat in the case of enclosure fires in large compartments. These methods range from manual calculations, based on empirical formulae, over zone modeling to the use of computational fluid dynamics. The focus is on large single storey compartments. The differences between results obtained with the examined methods are discussed. .
Test of total heat flux from wood crib fire in and outside compartment
Authors: Qiang Xu , Griffin Gregory , Preston Christopher , Bicknell Ashley , Bradbury Glenn , White Nathan
Published: July 2007

Woo d crib fires were studied by using of ISO 9705 Room. These free burning tests with different heat release rate were conducted inside room and outside room (under the hood). Thermal condition around crib fire was measured by using of thermocouples, total heat flux gauge, gas concentration analyzer, and standard instrumentations for heat release rate measurement in ISO 9705 Room. This paper focuses on the total heat flux to the surrounding area from wood crib fire. The correlation between heat release rate and total heat flux is presented. Wall and space effect is also analyzed.
Methodology of using CFD-based risk assessment in road tunnels
Authors: Vidmar Peter , Petelin Stojan
Published: July 2007

The definition of the deterministic approach in the safety analyses comes from the need to understand the conditions that come out during the fire accident in a road tunnel. The key factor of the tunnel operations during the fire is the ventilation, which during the initial fazes of the fire, impact strongly on the evacuation of people and latter on the access of the intervention units in the tunnel. The paper presents the use of the computational fluid dynamics model in the tunnel safety assessment process. The model is validated by comparing data with experimental and quantifying the differences. The set-up of the initial and boundary conditions and the requirement for grid density found during the validation tests is used to prepare three kind of fire scenarios 20 MW, 50 MW, and 100 MW, with different ventilation conditions; natural, semi transverse, full transverse, and longitudinal ventilation. The observed variables, soot density and temperature, are presented in minutes time steps trough the entire tunnel length. Comparing the obtained data in a table, allows the analyses of the ventilation conditions for different heat releases from fires. The second step is to add additional criteria of human behaviour inside the tunnel (evacuation) and human resistance to the elevated gas concentrations and temperature. What comes out is a fully deterministic risk matrix that is based on the calculated data where the risk is ranged on five levels, from the lowest to a very danger level. The deterministic risk matrix represents the alternative to a probabilistic safety assessment methodology, where the fire risk is represented in detail as well as the computational fluid dynamics model results are physically correct. .
Numerical simulation of fire spread in terminal 2 of Belgrade airport
Authors: Stevanovic Zarko , Markovic Zoran , Turanjanin Valentina
Published: July 2007

This paper concern the results of software fire spread process prototype in terminal 2 of Belgrade airport using computational fluid dynamics. Numerical simulation of fire for the most critical fire scenario has been performed, primarily obtaining the space and time distribution of: velocity, pressure, temperature, and smoke concentration, assuming that HVAC systems have been switched off and all doors on the evacuation ways have been opened, just as the fire started. Also, two simulations have been compared of the smoke ventilation and not ventilation for the same scenario. Within the framework of the results presentation, isosurfaces of constant temperature (100 ?C) and smoke concentration (4000 ppm) are presented, based on the numerical simulation. Progression of these surfaces along the terminal 2 coincides to the experimental and experience evidence, forming the plume zone just above the fireplace, and spreading in the zone of underground ceiling and stairwell openings. .
Determinants of PGA Tour Success: An Examination of Relationships among Performance, Scoring, and Earnings
Authors: Finley Peter S. , Halsey J. Jason
Published: July 2007

Professional Golf Association (PGA) statistics for the 2002 season were analyzed to estimate the relationships between performance variables, scoring, and earnings. Two newly considered variables, Scrambling and Bounce Back percentages, showed meaningful correlation to Simple Scoring Average ( rs = –.69 and –.40, respectively), and each made a significant contribution to a regression model. While the full model of performance variables explained most of the variance in Simple Scoring Average ( R2 = .94), an adjusted scoring figure, accounting for the performance of the full field of players in each round, better correlated with Earnings over a PGA Tour season ( r = .77).
Innovation and Imitation as Sources of Sustainable Competitive Advantage
Authors: Pérez‐Luño Ana , Valle Cabrera Ramón , Wiklund Johan
Published: July 2007

The present study fills some of the void in the literature on the concept and phenomenon of innovation and imitation. Basing our arguments on features that the literature indicates are characteristics of innovation, we delimit the concepts of innovation and imitation. Using these features and considering a company’s degree of entrepreneurial and market orientation, we devise a typology of companies ranging from radical innovators to strict imitators. We also argue that some key factors and the choice of appropriate strategy determine whether innovative and imitative companies can obtain and maintain their sustainable competitive advantages.
Innovation in Service Firms: Exploratory Analysis of Innovation Patterns
Authors: Dionisia Elche Hortelano María , Gongález‐Moreno Ángela
Published: July 2007

The aim of this paper is to contribute to the understanding of innovation in services. First, service firms were classified according to the degree of customization of service product and technology, because it reflects the degree of interaction between producer and consumer. This is a key element in the process of production and, hence, in the innovation developed by these firms. Second, we identified four different modes of innovation in Spanish service firms, which reflect diverse patterns of innovation according to depth of changes introduced by firms. Finally, we examined how the innovation patterns are generalized by the type of service firms, confirming that there is a relationship between production and innovation strategies. This paper yields empirical evidence from Spanish services, showing that service firms develop innovations coherently according to their production strategy.
Intra‐female aggression in the mouse (Mus musculus domesticus) is linked to the estrous cycle regularity but not to ovulation
Authors: Morè Lorenzo
Published: July 2007

Intraspecific communication between mice takes place mainly via urinary chemosignals or “pheromones”. Pheromones can influence aggressive and reproductive behavior as well as the neuroendocrine condition of the recipient female mice via their olfactory system. In this study, reproductively cyclic mice in the estrus phase were used to test intraspecific agonistic aggressive behavior. Data were obtained also on the count of the eggs shed in the oviducts. The results showed that (i) individually housed female mice are more aggressive toward an intruder female mouse than grouped mice, (ii) mice in which the vomeronasal organ was removed show aggressive behavior intermediate between individually housed and grouped mice, and (iii) a within group analysis did not show a positive correlation between aggression and presence of shed eggs in the oviducts. Aggr. Behav. 34:46–50, 2008. © 2007 Wiley‐Liss, Inc.
Robust track‐following control of hard disk drives using improved integral sliding mode combined with phase lead peak filter
Authors: Hu Qinglei , Xie Lihua , Wang Youyi , Du Chunling
Published: July 2007

An integral‐type sliding mode control (SMC) scheme with application to track‐following control in hard disk drives (HDDs) is investigated in this paper. With the proposed technique, the dynamics of the sliding mode is analytically obtained without any reaching phase by using the integral sliding surface. To reconstruct estimates of the system states for use in a full information SMC law, an asymptotic observer is also employed and the fulfillment of sliding condition, including the case when estimated states are used, is also verified. In addition, the proposed control scheme integrated with a phase lead peak filter (PLPF) is also investigated for better rejection of disturbance of narrow‐band type at mid‐frequency ranges. Simulation studies on the design of a track‐following controller in HDDs are conducted to illustrate its feasibility and effectiveness. The simulation results also demonstrate that the proposed scheme provides better performance than the conventional sliding mode and proportional–integral–derivative control methods. Copyright © 2007 John Wiley & Sons, Ltd.
Run‐to‐run control of membrane filtration processes
Authors: Busch Jan , Cruse Andreas , Marquardt Wolfgang
Published: July 2007

Membrane filtration processes are often operated cyclically, where one cycle comprises a filtration and a backwashing phase. Due to the complex mechanisms involved, these processes are mostly operated with fixed values of the manipulated variables, leaving much of the economical potential unexplored. A model‐based run‐to‐run process control approach is introduced, in which the manipulated variables are optimized after each filtration cycle. The approach is evaluated in a case study on submerged membrane filtration in wastewater treatment. A simple, computationally inexpensive process model is developed. The resulting model‐based controller is tested in a simulation environment employing a validated reference model. It yields excellent results with respect to prediction quality and optimization results. © 2007 American Institute of Chemical Engineers AIChE J, 2007
A new method to visualize and characterize the pore structure of TENCEL® (Lyocell) and other man‐made cellulosic fibres using a fluorescent dye molecular probe
Authors: Abu‐Rous Mohammad , Varga Ksenija , Bechtold Thomas , Schuster Kurt Christian
Published: July 2007

The internal porous structures of the man‐made cellulosic fibers Lyocell (TENCEL®), Modal, and Viscose fibers were visualized by applying fluorescence microscopy on fiber cross sections. The fiber pore structure was probed by the optical brightener Uvitex BHT, and the dye penetration depth was measured. The main differences in the pore structures of these three fiber types could be visualized. Only TENCEL shows a significant difference between dried and never‐dried fibers. A fiber structure model of TENCEL was obtained, which discriminates three different porous zones with respect to dye diffusion kinetics. The results are discussed in relationship with the fiber physical and chemical properties. The dye penetration depth and kinetics in TENCEL fibers was found to be sensitive to the production and treatment conditions, in particular to changes in the pore system by drying, and following alkali swelling processes. The performance of surface‐specific enzymatic peeling could also be observed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Preparation and characterization of novel poly(glycidyl methacrylate) beads carrying amidoxime groups
Authors: Çaykara Tuncer , Alaslan Şerife Ş.
Published: July 2007

Poly(glycidyl methacrylate) (PGMA) beads with an average size of 350 μm were synthesized by suspension polymerization technique. The PGMA beads were first modified with iminodiacetonitrile (IDAN). Then, the IDAN‐modified beads were subsequently modified by hydroxylamine. The IDAN modification and the conversion of the nitrile groups to amidoxime were followed by FT‐IR spectroscopy. The surface morphology and thermal behavior of the PGMA and its modified forms were also characterized by scanning electron microscopy and thermogravimetric analysis techniques, further confirming modification and amidoximation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Data cleansing for Web information retrieval using query independent features
Authors: Liu Yiqun , Zhang Min , Cen Rongwei , Ru Liyun , Ma Shaoping
Published: July 2007

Understanding what kinds of Web pages are the most useful for Web search engine users is a critical task in Web information retrieval (IR). Most previous works used hyperlink analysis algorithms to solve this problem. However, little research has been focused on query‐independent Web data cleansing for Web IR. In this paper, we first provide analysis of the differences between retrieval target pages and ordinary ones based on more than 30 million Web pages obtained from both the Text Retrieval Conference (TREC) and a widely used Chinese search engine, SOGOU (www.sogou.com). We further propose a learning‐based data cleansing algorithm for reducing Web pages that are unlikely to be useful for user requests. We found that there exists a large proportion of low‐quality Web pages in both the English and the Chinese Web page corpus, and retrieval target pages can be identified using query‐independent features and cleansing algorithms. The experimental results showed that our algorithm is effective in reducing a large portion of Web pages with a small loss in retrieval target pages. It makes it possible for Web IR tools to meet a large fraction of users' needs with only a small part of pages on the Web. These results may help Web search engines make better use of their limited storage and computation resources to improve search performance.
On optimal operating conditions for a data processing system: A stochastic approach
Authors: Cha Ji Hwan , Mi Jie
Published: July 2007

In this paper, we consider the problem of determining optimal operating conditions for a data processing system. The system is burned‐in for a fixed burn‐in time before it is put into field operation and, in field operation, it has a work size and follows an age‐replacement policy. Assuming that the underlying lifetime distribution of the system has a bathtub‐shaped failure rate function, the properties of optimal burn‐in time, optimal work size and optimal age‐replacement policy will be derived. It can be seen that this model is a generalization of those considered in the previous works, and it yields a better optimal operating conditions. This paper presents an analytical method for three‐dimensional optimization problem. An algorithm for determining optimal operating conditions is also given. Copyright © 2007 John Wiley & Sons, Ltd.
Recent advances in DNA catalysis
Authors: Höbartner Claudia , Silverman Scott K.
Published: July 2007

Studies of catalytically active DNA sequences have expanded considerably since the first artificial deoxyribozyme was identified in 1994. Nevertheless, the field is still quite young, and advances in both fundamental understanding and practical applications of deoxyribozymes are still developing. Deoxyribozymes that either cleave or ligate two RNA substrates have been most widely investigated, and this review describes recent advances in the fundamental studies and applications of these DNA enzymes. Deoxyribozymes with catalytic activities other than RNA ligation and cleavage are also increasingly pursued, and this review covers several key examples. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 279–292, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Polymerase Recognition and Stability of Fluoro‐Substituted Pyridone Nucleobase Analogues
Authors: Hwang Gil Tae , Leconte Aaron M. , Romesberg Floyd E.
Published: July 2007

Recently much effort has been focused on designing unnatural base pairs that are stable and replicated by DNA polymerases with high efficiency and fidelity. This work has helped to identify a variety of nucleobase properties that are capable of mediating the required interbase interactions in the absence of Watson–Crick hydrogen‐bonding complementarity. These properties include shape complementarity, the presence of a suitably positioned hydrogen‐bond donor in the developing minor groove, and fluorine substitution. In order to help characterize how each factor contributes to base pairing stability and replication, we synthesized and characterized three fluoro‐substituted pyridone nucleoside analogues, 3 FP, 4 FP, and 5 FP. Generally, we found that the specific fluorine substitution pattern of the analogues had little impact on unnatural pair or mispair stability, with the exception of mispairs with dG, which were also the most stable. The mispair between dG and 3 FP was less stable than that with 4 FP or 5 FP, which likely resulted from specific interbase interactions. While fluorine substitution had little impact on the synthesis of the unnatural base pairs, it significantly enhanced mispairing with dG. Remarkably, the mispair between dG and 3 FP was the most efficiently synthesized, due to a favorable entropy of activation, which possibly resulted from the displacement of water molecules from dG in the phosphoryl transfer transition state. The more efficient synthesis of the 3 FP–dG mispair, despite its being the least stable of the three, suggests that the determinants of synthesis and stability are distinct. Finally, we found that fluorine substitution significantly increased the rate at which the pyridone‐based unnatural base pairs were extended; this suggests that both minor groove hydrogen‐bond acceptors and fluorine substituents could be used to simultaneously optimize unnatural base pairs.
Homoscedastic controlled calibration model
Authors: Achic Betsabé G. Blas , Sandoval Mônica C. , Yoshida Olga Satomi
Published: July 2007

In the context of the usual calibration model, we consider the case in which the independent variable is unobservable, but a pre‐fixed value on its surrogate is available. Thus, considering controlled variables and assuming that the measurement errors have equal variances we propose a new calibration model. Likelihood‐based methodology is used to estimate the model parameters and the Fisher information matrix is used to construct a confidence interval for the unknown value of the regressor variable. A simulation study is carried out to asses the effect of the measurement error on the estimation of the parameter of interest. This new approach is illustrated with an example. Copyright © 2007 John Wiley & Sons, Ltd.
Trapping of Radicals in the Coordination Spheres of Metals
Authors: Hou Zhaomin , Wakatsuki Yasuo
Published: July 2007

The use of hexamethylphosphoramide (HMPA) or other sterically demanding groups as stabilizing ligands allows the successful isolation of a series of structurally characterizable complexes of ketyl radicals with alkali, alkaline earth, and lanthanide metal. It has been demonstrated that the stability and reactivity of the ketyl radicals strongly depend on both the nature of the metals to which they are bound and the steric and electronic properties of the ancillary ligands, as well as the structure of their parent ketones.
Design and Synthesis of Sugar‐Responsive Semiartificial Myoglobin Triggered by Modulation of Apoprotein–Cofactor Interactions
Authors: Hamachi Itaru , Tajiri Yusuke , Nagase Tsuyoshi , Shinkai Seiji
Published: July 2007

Phenylboronic acid groups as sugar recognition sites were successfully introduced into native myoglobin by a cofactor‐reconstitution method. Spectrophotometric pH titration demonstrated the sugar‐induced pKa shift of the H2O coordinated to the heme center of the semisynthetic myoglobin bearing phenyl‐boronic acids (met‐Mb(PhBOH)2). By means of circular dichroism (CD) and paramagnetic 1H NMR spectroscopies, it was proven that sugars that were bound to phenylboronic acid sites induced the rearrangement of the heme crevice to reinforce the heme cofactor‐apoprotein interactions. The structural changes that were induced by the binding of sugars subsequently enhanced the dioxygen storage activity of Mb(PhBOH)2. Such sugar‐induced structural and functional changes did not occur for other modified Mbs that had no sugar‐recognition units. Interestingly, a randomly modified Mb with phenylboronic acid units did not show any sugar response. In Mb(PhBOH)2, the information from the sugar‐binding event was efficiently transmitted to the active center, so that the activity was efficiently altered upon sugar binding. In conclusion, the active site specific incorporation of molecular recognition units as nonnatural functional molecules can provide a novel strategy for the design of stimuli‐responsive semisynthetic proteins.
Iceman's Mummification—Implications from Infrared Spectroscopical and Histological Studies
Authors: Bereuter Thomas L. , Mikenda Werner , Reiter Christian
Published: July 2007

A skin sample from the Iceman (Ötzi, Similaun Man, Man from Hauslabjoch) was studied by means of IR spectroscopy and histology, and the results were compared to those obtained from nine other more recent human tissue samples with known case reports. Attenuated total reflection IR spectroscopy was used for studying the fate of proteins and lipids in these rare skin tissues. This technique provided a simple yet powerful means for semiquantitative determination of the main compound classes found in skin samples, namely, triacylglycerols, their main breakdown products (fatty acids), and proteins. When combined with histology, IR spectroscopy provided reliable information about the main conditions under which mummification of the samples had taken place. In the case of the 5300‐year‐old Iceman, preserved collagen contributed to the conservation of morphological structures of the skin, although no cellular structures such as nuclei survived. In addition, post‐mortal alterations such as hydrolysis of triacylglycerols and phospholipids into fatty acids were unequivocally demonstrated. The solidified fatty acids provided a certain degree of preservation to the tissue characteristic of adipocere. Based on this observation, taken together with the concomitant loss of epidermis, we suggest that Iceman's body was submerged in water for a period of at least several months prior to desiccation. Results from other research disciplines support our conclusions.
Triprotonated Hydrogen Sulfide: Pentacoordinate Sulfonium Trication SH3+5 and the Search for its Parent Pentacoordinate Oxonium Trication OH3+5
Authors: Olah George A. , Rasul Golam , Surya Prakash G. K.
Published: July 2007

The pentahydridosulfonium trication SH3+5 was found by ab initio MP2/ 6‐31G** and QCISD(T)/6‐311G** levels of calculation to be a stable minimum with Cs symmetric structure 1. It is isostructural with the parent pentacoordinate carbonium ion CH+5. Structure 1 resembles a complex between SH3+3 and molecular hydrogen forming a 2e–3c bond. This structure involving a pentaco‐ordinate sulfur atom is unprecedented. Rotation of the H2 unit around the pseudo‐C3 axis of SH3 is facile. The structure of SF3+5 was also calculated and compared with that of 1. In addition, our studies at the ab initio MP2/6‐31G** level showed that the parent pentacoordinate oxonium trication OH3+5 is not a minimum on its potential energy surface, and dissociation into OH2+4 and H+ occurs upon optimization.
Reactive Pseudorotaxanes: Inclusion Complexation of Reduced Viologens by the Hosts β‐Cyclodextrin and Heptakis(2,6‐di‐o‐Methyl)‐β‐Cyclodextrin
Authors: Mirzoian Armen , Kaifer Angel E.
Published: July 2007

The complexation of three guests containing 4,4′‐bipyridinium redoxactive residues by β‐cyclodextrin (β‐CD) and its heptakis‐(2,6‐O‐dimethyl) analogue (DM‐β‐CD) was investigated by means of voltammetric techniques. The three 4,4′‐bipyridinium (viologen) derivatives used as guests were designed to be water‐soluble in all three accessible oxidation states. The N‐substituents chosen to enhance aqueous solubility were: 2‐(2‐(2‐ethoxy)ethoxy)ethanol (guest 12+), 6‐hexanoate (guest 2), and 3‐propanesulfonate (guest 3). Detailed analysis of the voltammetric results by digital simulation techniques revealed that the oxidized forms of the guests did not interact appreciably with either CD host; the two‐electron reduced guests formed extremely stable inclusion complexes, with association constants in the range 103–104M−1, while the cation radical forms exhibited intermediate binding affinities (≈︁102M−1). In all cases, DM‐β‐CD was found to form more stable complexes than unmodified β‐CD.
Indium‐Mediated Reactions of Enamines in the Presence of Acid
Authors: Tussa Laurent , Lebreton Chrystèle , Mosset Paul
Published: July 2007

The reaction of enamines with allyl bromide and metallic indium in THF to afford homoallylamines was greatly accelerated by the addition of one equivalent of a suitable carboxylic acid, such as acetic acid. It was established that the likely mechanism consists of a nucleophilic addition of an indium sesquihalide to the iminium salt formed by protonation of the enamine. Substituted allyl bromides also reacted with complete allylic transposition (γ‐addition). In contrast to indium‐mediated allylation of carbonyl compounds in which only two of the three allyl groups of the sesquihalide are involved, all three allyl groups are involved in the reaction with enamines. As a result only 2/3 equiv of indium are required. This allylation was also performed with zinc, tin, bismuth, and aluminum in the presence of a catalytic amount of InCl3 instead of indium. However, these reactions invariably gave lower yields. The analogous reaction of methyl bromoacetate instead of allyl bromide was also studied. This “Reformatsky‐type” process was also greatly accelerated by the addition of one equivalent of acetic acid. In this case, the yields remained moderate for both indium and zinc.
π‐Electron Ring‐Current Effects in Multiple Adducts of 3He@C60 and 3He@C70: A 3He NMR Study
Authors: Rüttimann Markus , Haldimann Richard F. , Isaacs Lyle , Diederich François , Khong Anthony , Jiménez‐Vázquez Hugo , Cross R. J. , Saunders Martin
Published: July 2007

Bis‐ to hexakisadducts of C60 (1–6) and mono‐ to tetrakisadducts of C70 (7–13) containing 3He atoms (endo‐hedral helium complexes) were prepared and studied by 3He NMR spectroscopy to determine the influence of degree of functionalization and addition pattern on the chemical shift of the 3He atom. In the series of C60 derivatives, which included the previously measured 6–6 monoadduct 3He@C61H2, the 3He resonance was shifted considerably upfield relative to that of 3He@C60 (δ = −6.36) up to the bisadduct 1 (δ = −11.45). The resonances of the higher adducts 3–6, however, were shifted only slightly further up‐field and all appeared in a rather narrow spectral range between δ = −11.84 and −12.26. The absence of further substantial upfield shifts was rationalized in terms of the compensation of deshielding due to the functionalization‐induced decrease in the diamagnetic π‐electron ring currents that extend around the fullerene sphere by the shielding that results from the weaker pentagonal‐ring paramagnetic currents and the increased number of localized benzenoid substructures in 3–6. In contrast, all 3He resonances of the C70 adducts are shifted downfield relative to the signal of 3He@C70 (δ = −28.81). A monotonic relationship exists between the chemical shift and the degree of functionalization, whereby the 3He chemical shifts steadily decrease from monoadduct 7 (δ = −27.53) to the isomeric tetrakisadducts 12 (δ = −21.09) and 13 (δ = −20.68). This deshielding was explained by the reduction of the strong diamagnetic ring currents extending along the polar corannulene perimeters as a result of the functionalization at α‐ and β‐type polar bonds in 7–13. In both series, the addition pattern was also found to have a distinct influence on the 3He chemical shift.
Effect of Melamine‐Amphiphile Structure on the Extent of Two‐Dimensional Hydrogen‐Bonded Networks Incorporating Barbituric Acid
Authors: Koyano Hiroshi , Bissel Philippe , Yoshihara Kanami , Ariga Katsuhiko , Kunitake Toyoki
Published: July 2007

Four alkyl melamine amphiphiles each containing identical triads of hydrogen‐bonding sites (hydrogen donor, acceptor, and donor) but different numbers of alkyl chains were examined in order to determine their monolayer properties and binding behavior towards barbituric acid (BA). Their structural organization in supramolecular assemblies at the air–water interface was affected by the bulkiness of the hydrophobic part of the amphiphile. Aqueous BA and amphiphiles with two or three alkyl chains formed a 1:1 alternate network structure. In contrast, a melamine amphiphile with four alkyl chains formed a 2:1 (BA:amphiphile) complex rather than a 1:1 alternate network structure. The 2:1 complex appears to behave like an independent molecular entity without further networking. The results point to the importance of size matching between the hydrophobic part of the monolayer and the underlying hydrogen‐bonded network in order to maintain the overall supramolecular structure.
A Comparative Study of Oxo‐Ligand Effects in the Gas‐Phase Chemistry of Atomic Lanthanide and Actinide Cations
Authors: Cornehl Hans H. , Wesendrup Ralf , Diefenbach Martin , Schwarz Helmut
Published: July 2007

The effects of oxo ligands on lanthanide and actinide cations have been examined for the mono‐ and dioxocations MO+ and MO+2 of cerium, neodymium, thorium, and uranium by probing C‐H and C‐C bond activation of hydrocarbons in an FT‐ICR mass spectrometer. The metal monoxide cations are readily available by reaction of the “bare” metal cations with O2, CO2, N2O, or H2O. In the ensuing oxidation of MO+, UO+2 is obtained by each of these oxidants, while CeO+ could only be oxidized by N2O. NO2 was necessary for the generation of ThO+2, and NdO+2 could not be prepared at all. The monoxides are rather unreactive and only dehydrogenate reactive substrates such as 1‐butene and 1,4‐cyclohexadiene to generate the corresponding butadiene or benzene complexes. In contrast, CeO+2 and ThO+2 react efficiently with different substrates by abstraction of a hydrogen atom and formation of the closed‐shell species OMOH+, or by oxygen atom transfer to unsaturated hydrocarbons. In marked contrast, UO+2 only undergoes very slow adduct formation with unsaturated hydrocarbons. The results are compared with the reactions of the “bare” metals with respect to the influence of the oxo ligand as well as to the underlying electronic features of the investigated complexes.
Large Quadratic Hyperpolarizabilities with Donor–Acceptor Polyenes Exhibiting Optimum Bond Length Alternation: Correlation Between Structure and Hyperpolarizability
Authors: Blanchard‐Desce M. , Alain V. , Bedworth P. V. , Marder S. R. , Fort A. , Runser C. , Barzoukas M. , Lebus S. , Wortmann R.
Published: July 2007

Donor–acceptor polyenes of various lengths, and that combine aromatic electron‐donating moieties with powerful heterocyclic electron‐withdrawing terminal groups, have been synthesized and characterized as efficient nonlinear optical (NLO) chromophores. Their linear and nonlinear optical properties have been investigated, and variations in these properties have been related to ground‐state polarization (dipole μ) and structure. In particular, unprecedented quadratic hyperpolarizabilities (β) have been achieved (up to β(0) = 1500 × 10−30 esu) by reduction of the bond‐length alternation (BLA) in the polyenic chain. In each series of homologous compounds, increasing the number n of conjugated double bonds in the polyenic chain results in a marked bathochromic shift, more pronounced BLA, and exponential increases in μβ(0) values. As a result, polyenic chromophores displaying excellent optical quadratic nonlinearities (μβ values as large as 100 times that of the quadratic NLO benchmark 4‐dimethyl‐amino‐4′‐nitrostilbene (DANS)), as well as satisfactory solubility, have been obtained.
Dicyanopolyynes: A Homologuous Series of End‐Capped Linear sp Carbon
Authors: Schermann Günther , Grösser Thomas , Hampel Frank , Hirsch Andreas
Published: July 2007

The synthesis, isolation, spectroscopic characterization, and computational investigations of the rod‐shaped dicyanopolyynes 1–6 (C2nN2, n = 4–9), which are model substances for the hypothetical one‐dimensional carbon allotrope carbyne sp‐C∞, are described. Based on the trends in the spectroscopic behavior of 1–6 with increasing chain length, the electronic as well as the NMR properties of carbyne are predicted. For the investigation of the synthetic potential of this compound class, a first selected series of regioselective derivatizations is presented with the synthesis of the [4+2] and [3+2] cycloadducts 7–12.