bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetisch unbestimmte Systeme
Authors: Grammel R.
Published: May 2007

Dem Begriffe des statisch unbestimmten Systems hat L. Prandtl den Begriff des elastisch unbestimmten Systems an die Seite gestellt. Von der Statik zur Kinetik fortschreitend kommt man auf den weiteren Begriff der kinetisch unbestimmten Systeme. Darunter verstehe ich solche, deren Bewegung sich mit den Grundgesetzen der Stereokinetik überhaupt nicht ermitteln läßt, oder, etwas genauer gesagt: für deren Bewegung die Stereokinetik unendlich viele Lösungen liefert, unter denen die tatsächlich eintretende nur dann gefunden werden kann, wenn man die Idee des starren Körpers aufgibt, Systeme also, die den Geltungsbereich der Idee des starren Körpers ebenso überschreiten, wie dies die statisch unbestimmten Systeme in ihrer Art tun. Kinetisch unbestimmte Systeme in diesem Sinne kommen vereinzelt in der Mechanik schon lange vor (z. B. der “halbelastische” Stoß zweier “starrer” Körper, wobei die fehlende kinetische Gleichung durch die phänomenologische Annahme einer nur stoffabhängigen Stoßzahl ersetzt wird); aber systematisch scheint dieser Begriff bis jetzt nicht untersucht worden zu sein. Im folgenden will ich einige der wichtigsten Klassen von kinetisch unbestimmten Systemen aufzählen und durch Beispiele belegen.
Das Falten des Randes beim Pressen von Schalen
Authors: Willers Fr. A.
Published: May 2007

Für die Anzahl der Wellen, die an dem schmalen Rande kreisrunder, zu Schalen gepreßter Scheiben auftreten, wird mittels des Ritzschen Verfahrens eine Näherungsformel abgeleitet.
Prevalence of feline chronic gingivo-stomatitis in first opinion veterinary practice
Authors: Healey Katharine AE , Dawson Susan , Burrow Rachel , Cripps Peter , Gaskell Christopher J. , Hart C Anthony , Pinchbeck Gina L , Radford Alan D. , Gaskell Rosalind M
Published: May 2007

Feline chronic gingivo-stomatitis (FCGS) is a syndrome characterised by persistent, often severe, inflammation of the oral mucosa. In the absence of similar studies, our objective was to estimate the prevalence of FCGS in a convenience based sample of cats visiting first opinion small animal veterinary practices. Twelve practices took part, providing a sample population of 4858 cats. Veterinary surgeons identified cases of FCGS according to our case definition over a 12-week sampling period; age, sex and breed information was determined for all cats, plus brief descriptive data for FCGS cases. The prevalence of FCGS was 0.7% (34 cases, 95% confidence intervals: 0.5–1.0%). Of the 34 cases of FCGS, 44% (15 cats) were new cases and 56% (19 cats) were ongoing cases. No statistically significant difference ( P>0.353) was found when the age, sex and breed of cats with FCGS were compared to data from cats without the condition.
Association between juvenile reef fish and the Caribbean reef squid Sepioteuthis sepioidea on north-eastern Brazilian coastal reefs
Authors: Nunes José de Anchieta C.C. , Chaves Laís de C.T. , Maia-Nogueira Rodrigo , Sampaio Cláudio L.S.
Published: May 2007

This article reports on four different juvenile reef fish species, Polydactylus virginicus, Haemulon aurolineatum,
H. steindachneri and Carangoides bartholomaei swimming along with schools of the caribbean reef squid
Sepioteuthis sepioidea. Three different behaviours were observed. This is the first record of this squid species
on Brazilian reef habitats. We suggest that this behaviour is mainly related to protection for juvenile fish
against potential pelagic predators.
Phenotypic variability associated with the occurrence of imposex in Odontocymbiola magellanica from Golfo Nuevo, Patagonia
Authors: Bigatti Gregorio , Carranza Alvar
Published: May 2007

The increasing occurrence of imposex in marine gastropods has been related to their exposure to the
tri-substituted organotin compounds tributyltin (TBT) and triphenyltin (TPhT), which have been widely
used as antifouling agents, and has been documented for more than 200 gastropod species. Odontocymbiola
magellanica, a large benthic neogastropod, showed 85–100% imposex near harbours with high marine
traffic in Patagonia. We evaluated if, as predicted by the energy allocation hypothesis, females with
imposex (FWI) were on average larger and/or heavier than normal individuals, and if there were differences
in shell morphometry associated with imposex, using both univariate and multivariate approaches.
We detected differences in two morphometric variables, but no overall effect in shell shape, and ~10% of
reduction in body weight in FWI. In addition, the multivariate index of size suggested a positive effect on
FWI, in contrast to univariate analyses showing no differences in shell length. The present results demonstrate
that responses to TBT vary among gastropod species and that the energy allocation hypothesis may
be useful only under certain conditions.
Ammonia emissions from seabird colonies
Authors: Blackall Trevor D. , Wilson Linda J. , Theobald Mark R. , Milford Celia , Nemitz Eiko , Bull Jennifer , Bacon Philip J. , Hamer Keith C. , Wanless Sarah , Sutton Mark A.
Published: May 2007

Ammonia emissions were measured from two entire seabird colonies with contrasting species assemblages, to ascertain the ammonia volatilisation potentials among seabird species in relation to their nesting behaviour. Emissions were calculated from downwind plume measurements of ammonia concentration using both inverse dispersion and tracer ratio methods. Measured colony emissions ranged 1–90 kg NH3 hour−1, and equated to 16 and 36% volatilization of excreted nitrogen for colonies dominated by ground/burrow nesting and bare rock nesting birds, respectively. The results were applied in a bioenergetics model with a global seabird database. Seabird colonies are found to represent the largest point sources of ammonia globally (up to ∼6 Gg NH3 colony−1 year−1). Moreover the largest emissions occur mainly in remote environments with otherwise low NH3 emissions. These ammonia “hot spots” explain significant perturbations of the nitrogen cycle in these regions and add ∼20% to oceanic ammonia emissions south of latitude 45°S.
Information gain of a model based on multidisciplinary observations with correlations
Authors: Imoto Masajiro
Published: May 2007

Utsu, Aki, and others have formulated earthquake probabilities on the basis of precursory anomalies in multidisciplinary observations, assuming that occurrences of one kind of precursory anomaly are independent from those of another. We extend their studies to cases where precursory anomalies depend on one another. We consider two kinds of distributions for each precursory parameter, those associated with only space‐time volumes in the vicinity of target events (conditional density distributions) and those associated with space‐time volumes not including target events within a short distance (background density distributions). Treating precursory anomalies as continuous variables, we assume that the conditional and background densities from each discipline are normally distributed. We obtain analytical solutions for the general case in which mutual correlations exist among precursory anomalies in both distributions. First, we consider the case in which observations are correlated with one another in the conditional density distribution but not in the background density distribution, and then the case in which observations are correlated in both distributions. The result obtained in the first case is compared with cases in which the observations are independent of one another in both distributions. This comparison leads to the conclusion that the mean probability gain is always larger in the correlated case than in the independent case. The ratio of the former to the latter is expressed in terms of correlation coefficients and becomes infinitely large when the absolute value of the correlation coefficient approaches 1. Analytical solutions for the two‐dimensional case are given in an explicit form. Applying these solutions to distributions of the Gutenberg‐Richter a and b values observed in Kanto, Japan, we obtained a combined model with a and b values that outperform either model of the Gutenberg‐Richter relation, with a universal b value or a variable one. These findings could be applied in combining a wide range of multidisciplinary observations into a single model of earthquake probability.
Bayesian merging of multiple climate model forecasts for seasonal hydrological predictions
Authors: Luo Lifeng , Wood Eric F. , Pan Ming
Published: May 2007

This study uses a Bayesian approach to merge ensemble seasonal climate forecasts generated by multiple climate models for better probabilistic and deterministic forecasting. Within the Bayesian framework, the climatological distribution of the variable of interest serves as the prior, and the likelihood function is developed with a weighted linear regression between the climate model hindcasts and the corresponding observations. The resulting posterior distribution is the merged forecast, which represents our best estimate of the variable, including its mean and variance, given the current model forecast and knowledge about the model’s performance. The handling of multimodel climate forecasts and nonnormal distributed variables, such as precipitation, are two important extensions toward the application of the Bayesian merging approach for seasonal hydrological predictions. Two examples are presented as follows: seasonal forecast of sea surface temperature over equatorial Pacific and precipitation forecast over the Ohio River basin. Cross validation of these forecasts shows smaller root mean square error and smaller ranked probability score for the merged forecast as compared with raw forecasts from climate models and the climatological forecast, indicating an improvement in both deterministic and probabilistic forecast skills. Therefore there is great potential to apply this method to seasonal hydrological forecasting.
Interannual solar and net radiation trends in the Canadian Arctic
Authors: Weston Scott T. , Bailey William G. , McArthur L. J. Bruce , Hertzman Owen
Published: May 2007

Net and solar radiation trends over the past half‐century at Alert and Resolute Bay, Nunavut, are presented and analyzed. Substantive changes to the Canadian Arctic climate are observed over the data record. Decreases of 2.25% and 2.50% per decade in solar radiation are observed at Alert and Resolute Bay, respectively. An exploration of cloudless‐day radiation data suggests that this trend is likely driven by changes in atmospheric constituents. Even more significant overall increases in net radiation of 26.7% and 17.9% of the overall mean value per decade are measured at the respective locations, with those changes concentrated in the months of May and June. Exploration of annual and interannual albedo data reflects this result in earlier snowmelt dates and longer snow‐free periods. Evidence is presented showing that, in addition to increased temperatures, changes to the snowmelt date are being driven by increases in winter incoming longwave radiation. Resulting increased totals of net longwave radiation provide enhanced energy for snowmelt, thereby decreasing annual average albedo and increasing annual totals of net radiation. A persistently positive phase of the Arctic Oscillation in the mid‐1990s countered this overall trend and resulted in lower net radiation values. In this period, decreased stratospheric temperatures from an enhanced polar vortex drove decreased snowmelt and lower annual totals of net radiation.
Fokker-Planck modeling of current penetration during electron cyclotron current drive
Authors: Merkulov A. , Westerhof E. , Schüller F. C.
Published: May 2007

The current penetration during electron cyclotron current drive (ECCD) on the resistive time scale is studied with a Fokker-Planck simulation, which includes a model for the magnetic diffusion that determines the parallel electric field evolution. The existence of the synergy between the inductive electric field and EC driven current complicates the process of the current penetration and invalidates the standard method of calculation in which Ohm’s law is simply approximated by j−jcd=σE. Here it is proposed to obtain at every time step a self-consistent approximation to the plasma resistivity from the Fokker-Planck code, which is then used in a concurrent calculation of the magnetic diffusion equation in order to obtain the inductive electric field at the next time step. A series of Fokker-Planck calculations including a self-consistent evolution of the inductive electric field has been performed. Both the ECCD power and the electron density have been varied, thus varying the well known nonlinearity parameter for ECCD Prf[MW∕m−3]∕ne2[1019m−3] [R. W. Harvey et al., Phys. Rev. Lett 62, 426 (1989)]. This parameter turns out also to be a good predictor of the synergetic effects. The results are then compared with the standard method of calculations of the current penetration using a transport code. At low values of the Harvey parameter, the standard method is in quantitative agreement with Fokker-Planck calculations. However, at high values of the Harvey parameter, synergy between ECCD and E‖ is found. In the case of cocurrent drive, this synergy leads to the generation of large amounts of nonthermal electrons and a concomitant increase of the electrical conductivity and current penetration time. In the case of countercurrent drive, the ECCD efficiency is suppressed by the synergy with E‖ while only a small amount of nonthermal electrons is produced.
Growth and magnetic properties of Fe films epitaxially grown on Pd/Cu(001) by pulsed laser deposition
Authors: Lu Y. , Przybylski M. , Wang W. H. , Yan L. , Shi Y. , Barthel J. , Kirschner J.
Published: May 2007

We have grown Fe films on an epitaxial Pd monolayer on Cu(001) single crystals at room temperature, both Fe and Pd by pulsed laser deposition. The presence of the Pd interlayer influences growth, structure, and magnetism of the Fe films. Up to the thickness of 1.6 ML the Fe films show an out-of-plane easy axis of magnetization which changes to in-plane above. A linear dependence of the longitudinal Kerr rotation on the Fe thickness is obtained despite existing structural transformations. A strong increase of the Curie temperature TC is observed for the Fe films on Pd/Cu(001) compared to the Fe films grown directly on Cu(001). A correlation of the magnetic properties with possible structural changes and the role of Pd monolayer is discussed.
Source/drain-tied poly-Si thin-film transistor with π-shaped active region for device reliability improvement
Authors: Eng Yi-Chuen , Lin Jyi-Tsong
Published: May 2007

This article presents a nonclassical poly-Si thin-film transistor for device reliability improvement. With this structure, the discontinuous block oxide islands under the channel and the source/drain regions can help construct a natural source/drain tie to overcome the effects of floating-body and self-heating, respectively. In addition, both the junction leakage current and short-channel effects are significantly diminished in the proposed structure. For the most part, this is because the charge sharing from the source/drain junctions is blocked from entering the depletion region; hence, the controllability of the gate over the channel can be improved.
O
H
(
A
Σ
+
2
)
and rare gas-deuteride (NeD, ArD) excimers generated in microcavity plasmas: Ultraviolet emission spectra and formation kinetics
Authors: Ricconi B. J. , Park S.-J. , Sung S. H. , Tchertchian P. A. , Eden J. G.
Published: May 2007

Emission in the ultraviolet from the AΣ+2 electronic excited states of OH, NeD, and ArD, and the formation kinetics of these excited heteronuclear diatomics, have been investigated in microcavity plasmas generated in rare gas/H2O or D2 gas mixtures. Excitation transfer from the aΣu+3(1u,0u−) Rydberg state of Ar2 appears to be the dominant pathway to OH(AΣ+2) formation in Ar∕H2O vapor mixtures with total pressures of 400–800Torr and H2O partial pressures of 100mTorr–3Torr. Maximum emission on the (v′,v″)=(0,0) vibrational band of the OH(A→X) transition is observed in a 25μm, 45nl microcavity for 600–800Torr Ar∕0.5Torr H2O mixtures. Comparisons of experimental and simulated fluorescence spectra show the OH[AΣ+2(v′=0)] state rotational temperature to be 425K for 600Torr Ar∕100mTorr H2O mixtures but to rise linearly with the H2O partial pressure and exhibit a slope of 170K∕Torr H2O for 100mTorr⩽pH2O⩽3Torr. Excitation of Ne or Ar∕D2 gas mixtures in 50×50 arrays of Si microplasma devices generates broadband spectra, peaking in the mid-ultraviolet (λ∼280–320nm), which are attributed to the A→X transition of the ArD or NeD excimers. The optimal D2 concentration is observed to be ∼0.5% and the primary kinetic formation mechanism for the deuterides involves D atom transfer in collisions between Ar(4sP3) and D2.
Wave propagation characteristics of a figure-eight shaped nanoaperture
Authors: Eom G. S. , Yang D. , Lee E. , Park S. , Lee Y. , Hahn J. W.
Published: May 2007

Wave propagation characteristics of apertures were analyzed to explain the light transmission of metallic nanoapertures. Based on Maxwell’s equations, the wave dispersion relations of wave propagation modes in nanoapertures were derived. The resonance frequency shift of the aperture and the variation of the spot size are explained with the dispersion relations. The relationship between near-field and far-field light transmission power throughput and spot size is also shown with the wave mode change predicted by the dispersion relations.
Droplet dynamics in a microchannel subjected to electrocapillary actuation
Authors: Chakraborty Suman , Mittal Rajat
Published: May 2007

In this paper, a theoretical approach is devised to analyze the droplet dynamics in a microchannel subjected to electrocapillary actuation mechanisms. Specific attention is devoted to estimate the influences of the applied potentials and the hydrophobic insulation thicknesses, so as to obtain suitable interelectrode spacings, for a given droplet size. It is revealed that there exists a threshold limit on the value of the interelectrode pitch, beyond which the overall microfluidic transport rates are substantially lowered. On the other hand, with interelectrode spacings below the threshold limit, unnecessarily large number of electrodes might be necessary to achieve a desired droplet transport. Further, the optimal interelectrode spacings are found to be strong functions of the applied potentials and the dielectric layer thicknesses, based on which suitable design guidelines can be proposed.
Excitation-wavelength-dependent photoluminescence evolution of CdSe∕ZnS nanoparticles
Authors: Ozasa Kazunari , Nemoto Shigeyuki , Maeda Mizuo , Hara Masahiko
Published: May 2007

The wavelength-dependent photoluminescence (PL) evolution of CdSe∕ZnS (core/shell) nanoparticles (NPs) was investigated from the viewpoint of excitation wavelength dependence. In addition, the mechanisms involved in the photoinduced changes of the NP PL spectrum are discussed. The NPs of CdSe∕ZnS placed on a thin film of an insulator (GaAsOx∕GaAs or SiO2∕Si) exhibited PL decay and blueshifts on a time scale of minutes depending on the excitation wavelength, i.e., higher photon energy induces a faster PL decay with a larger and faster blueshift. The PL decay with 435nm excitation was a single exponential in temporal evolution, while the delayed acceleration of decay was observed with 365nm excitation. The excitation-wavelength dependence of the blueshift was much larger than that of the PL decay, indicating that they originate from independent photoinduced reactions. This was confirmed by an ultrahigh vacuum measurement where only PL decay was observed without any blueshift. This result clearly reveals that the blueshift is caused by photoinduced oxidation with atmospheric oxygen. Similar temporal PL evolutions were observed in single-NP measurements as gradual changes in colors. The most probable mechanism for PL decay is the photoinduced extraction of surface-protecting molecules from the NPs, which induces nonradiative recombinations of photoexcited electron-hole pairs.
Correlation between luminescence and structural evolution of Si-rich silicon oxide film annealed at different temperatures
Authors: Wang Minghua , Yang Deren , Li Dongsheng , Yuan Zhizhong , Que Duanlin
Published: May 2007

The visible red band light emission of the Si-rich silicon oxide films prepared by electron-beam evaporation with postannealing was investigated. The films annealed at temperatures lower than 600°C were composed of Si nanoclusters with high fraction of boundary atoms, featuring photoluminescence (PL) band centered at 700–710nm. By contrast, the PL bands of the films annealed at temperatures higher than 600°C redshifted with the expansion of the Si nanoclusters. The most intense light emission was observed in the 600°C annealed sample. The conversion of the luminescence mechanism from surface states controlled to quantum confinement controlled was proposed on the basis of the evolution of the film structure.
Atomic-scale flattening of SiC surfaces by electroless chemical etching in HF solution with Pt catalyst
Authors: Arima Kenta , Hara Hideyuki , Murata Junji , Ishida Takeshi , Okamoto Ryota , Yagi Keita , Sano Yasuhisa , Mimura Hidekazu , Yamauchi Kazuto
Published: May 2007

The authors present a method for flattening SiC surfaces with Pt as a catalyst in HF solution. The mechanism for flattening SiC surfaces is discussed. The flattened 4H-SiC(0001) surface is composed of alternating wide and narrow terraces with single-bilayer-height steps, which are induced by the rate difference of the catalytic reactions between adjacent terraces. Scanning tunneling microscopy images reveal a 1×1 phase on the terraces. The 1×1 phase is composed of coexisting of F- and OH-terminated Si atoms, which originate from the polarization of the underlying Si–C bonds.
Tailored polymer microlenses on treated glass surfaces
Authors: Sokuler Mordechai , Aronov Daniel , Rosenman Gil , Gheber Levi A.
Published: May 2007

Integrating arrayed biosensors (biochips) or micro- and nanofluidic devices with readout systems is an important step towards their realization in lab-on-a-chip devices. To this end, we present a straightforward method of fabricating polymer microlenses in precise locations, with desired optical characteristics, using a combination of two methods: surface energy tuning using low-energy electron irradiation, to control the numerical aperture, and time-controlled nanofountain pen deposition of polymer microlenses, to control the focal length. The authors demonstrate the tuning of focal length between 8 and 20μm with numerical apertures between 0.16 and 0.26.
Torsional behavior of chiral single-walled carbon nanotubes is loading direction dependent
Authors: Chang Tienchong
Published: May 2007

The torsion of carbon nanotubes is studied by molecular dynamics simulations. The torsional behavior of a chiral single-walled carbon nanotube (SWCNT) is dependent on the loading directions due to its structural asymmetry. The critical buckling shear strain of a SWCNT in one direction may be 1.8 times higher than that in the opposite direction. This means that one can choose the most appropriate SWCNT for his special purpose in designing a torsional component (e.g., oscillators and springs) of nanomechanical devices using carbon nanotubes. Meanwhile, the finding indicates that a simple thin shell model is not suitable for predicting torsional behavior of small SWCNTs at large strains.
Improved efficiency of zinc phthalocyanine/C60 based photovoltaic cells via nanoscale interface modification
Authors: Hong Z. R. , Maennig B. , Lessmann R. , Pfeiffer M. , Leo K. , Simon P.
Published: May 2007

The photovoltaic performance of zinc phthalocyanine (ZnPc)∕C60 heterojunctions is improved by alternately depositing ultrathin active layers between the two bulk layers. Using a proper multilayer structure, a 60% improvement in conversion efficiency under AM1.5 illumination is obtained, in comparison with that of flat heterojunctions. Transmission electron microscope investigations reveal an effective phase separation of ZnPc and C60 and a high degree of crystalline ordering of C60 in this system. The authors propose that an interpenetrating interface is formed, which facilitates both exciton separation and charge transport, and enhances the photocurrent from ZnPc due to an extended photoactive region.
Electrical polarizability of carbon nanotubes in liquid suspension
Authors: Brown Matthew S. , Shan Jerry W. , Lin Chen , Zimmermann Frank M.
Published: May 2007

The alignment and polarizability of single-wall carbon nanotubes in dilute ethanol suspensions under low-frequency, alternating-current electric fields were investigated through optical polarimetry. The nematic order parameter was determined by measuring changes in the state of polarization of a laser beam transmitted through the sample. The dependence of the measured alignment on the electric field was found to be consistent with a thermal-equilibrium distribution of freely rotating, polarizable rods. The polarizability determined by fitting to this model is consistent with the classical result for a conducting ellipsoid of the dimensions of the nanotubes.
Therapeutic Landscapes in Hospital Design: A Qualitative Assessment by Staff and Service Users of the Design of a New Mental Health Inpatient Unit
Authors: Curtis Sarah , Gesler Wil , Fabian Kathy , Francis Susan , Priebe Stefan
Published: May 2007

This pilot research project sought to provide a postoccupation assessment of a new mental health inpatient unit in East London, built under the Private Finance Initiative scheme. Qualitative discussion groups or unstructured interviews were used to explore the views of people who had been service users (but were currently well) and of nursing staff and consultants working in the new hospital. The participants gave their views on the aspects of the hospital which were beneficial or detrimental to well-being and the reasons for their views. Informants discussed hospital design in terms of: (1) respect and empowerment for people with mental illness; (2) security and surveillance versus freedom and openness; (3) territoriality, privacy, refuge, and social interactions; (4) homeliness and contact with nature; (5) places for expression and reaffirmation of identity, autonomy, and consumer choice; and (6) integration into sustainable communities. Themes emerging from this research were interpreted in light of ideas from geographical research on therapeutic landscapes constituted as physical, social, and symbolic spaces, as well as research from environmental psychology. The findings have practical implications for hospital design and underline the need to consider empowerment of patients in decisions over hospital design. We note the challenges involved in determining therapeutic hospital design given changing models of care in psychiatry, lack of consensus over models of care, and the varying and somewhat conflicting requirements these imply for the physical, social, and symbolic attributes of design of hospital spaces. We also note the implications of our findings for an interpretation of therapeutic landscapes as contested spaces.
Metabolic targeting of hypoxia and HIF1 in solid tumors can enhance cytotoxic chemotherapy
Authors: Cairns Rob A. , Papandreou Ioanna , Sutphin Patrick D. , Denko Nicholas C.
Published: May 2007

Solid tumors frequently contain large regions with low oxygen concentrations (hypoxia). The hypoxic microenvironment induces adaptive changes to tumor cell metabolism, and this alteration can further distort the local microenvironment. The net result of these tumor-specific changes is a microenvironment that inhibits many standard cytotoxic anticancer therapies and predicts for a poor clinical outcome. Pharmacologic targeting of the unique metabolism of solid tumors could alter the tumor microenvironment to provide more favorable conditions for anti-tumor therapy. Here, we describe a strategy in which the mitochondrial metabolism of tumor cells is increased by pharmacologic inhibition of hypoxia-inducible factor 1 (HIF1) or its target gene pyruvate dehydrogenase kinase 1 (PDK1). This acute increase in oxygen consumption leads to a corresponding decrease in tumor oxygenation. Whereas decreased oxygenation could reduce the effectiveness of some traditional therapies, we show that it dramatically increases the effectiveness of a hypoxia-specific cytotoxin. This treatment strategy should provide a high degree of tumor specificity for increasing the effectiveness of hypoxic cytotoxins, as it depends on the activation of HIF1 and the presence of hypoxia, conditions that are present only in the tumor, and not the normal tissue.
Subunit-specific Contribution of Pore-forming Domains to NMDA Receptor Channel Structure and Gating
Authors: Sobolevsky Alexander I. , Prodromou Michael L. , Yelshansky Maria V. , Wollmuth Lonnie P.
Published: May 2007

N-methyl-d-aspartate receptors (NMDARs) are ligand-gated ion channels that contribute to fundamental physiological processes such as learning and memory and, when dysfunctional, to pathophysiological conditions such as neurodegenerative diseases, stroke, and mental illness. NMDARs are obligate heteromultimers typically composed of NR1 and NR2 subunits with the different subunits underlying the functional versatility of NMDARs. To study the contribution of the different subunits to NMDAR channel structure and gating, we compared the effects of cysteine-reactive agents on cysteines substituted in and around the M1, M3, and M4 segments of the NR1 and NR2C subunits. Based on the voltage dependence of cysteine modification, we find that, both in NR1 and NR2C, M3 appears to be the only transmembrane segment that contributes to the deep (or voltage dependent) portion of the ion channel pore. This contribution, however, is subunit specific with more positions in NR1 than in NR2C facing the central pore. Complimentarily, NR2C makes a greater contribution than NR1 to the shallow (or voltage independent) portion of the pore with more NR2C positions in pre-M1 and M3-S2 linker lining the ion-conducting pathway. Substituted cysteines in the M3 segments in NR1 and NR2C showed strong, albeit different, state-dependent reactivity, suggesting that they play central but structurally distinct roles in gating. A weaker state dependence was observed for the pre-M1 regions in both subunits. Compared to M1 and M3, the M4 segments in both NR1 and NR2C subunits had limited accessibility and the weakest state dependence, suggesting that they are peripheral to the central pore. Finally, we propose that Lurcher mutation-like effects, which were identified in and around all three transmembrane segments, occur for positions located at dynamic protein–protein or protein–lipid interfaces that have state-dependent accessibility to methanethiosulfonate (MTS) reagents and therefore can affect the equilibrium between open and closed states following reactions with MTS reagents.
Tissue‐Engineered Bone Formation With Gene Transfer and Mesenchymal Stem Cells in a Minimally Invasive Technique
Authors: Park Dong‐Joon , Choi Jin Hyun , Leong Kam W. , Kwon Jang‐Woo , Eun Hee Seog
Published: May 2007

Background: The objective of this study was to use a chitosan‐alginate gel to implant bone marrow‐derived mesenchymal stem cells subcutaneously in a minimally invasive manner and promote bone formation by the simultaneously transferred osteogenic protein (OP)‐1 (bone morphogenic protein‐7) gene.

Method and Results: The complex of polyethylenimine/luciferase plasmid DNA embedded in the gel was able to transfect HEK 293 cells on a culture dish or co‐encapsulated in the gel. When injected into the subcutaneous space of mice, luciferase expression was two to three orders of magnitude increased above the background. To examine the efficacy of gene‐, cell‐, and combined gene‐ and cell‐encapsulated gels in tissue generation, samples were injected into the subcutaneous space of 6‐week‐old athymic nude mice, and the OP‐1 plasmid was studied. At 8 weeks after the injection, the gels only maintained their volumetric shape when human mesenchymal stem cells (hMSCs) were encapsulated, but otherwise the gels were partially dissolved. Transgene expression of OP‐1 was clearly detected in the samples after 4 weeks but not after 8 weeks. Type II collagen was detected in all the gels containing the OP‐1 plasmid, with or without hMSCs. The samples with the combination of OP‐1 DNA and hMSCs revealed strong type II collagen expression as well as osteoid foci.

Conclusion: These results suggest that combined gene and hMSC delivery within a chitosan‐alginate gel could be an interesting approach for tissue engineering.
Evolution of an avian pigmentation gene correlates with a measure of sexual selection
Authors: Nadeau Nicola J , Burke Terry , Mundy Nicholas I
Published: May 2007

The extravagant plumage traits of male birds are a favourite example of sexual selection. However, to date the units that selection is acting upon, the genes themselves have been a ‘black box’. Here, we report evidence of change driven by sexual selection at a pigmentation gene locus in the galliform birds. Across species, we find a correlation between the rate of amino acid change (dN/dS) at this locus (MC1R) and the degree of sexual dichromatism, which we use as a measure of the strength of sexual selection. There is no evidence for a similar pattern in any of five other loci (four candidate and one control locus). This is consistent with previous work on colour polymorphisms and suggests thatMC1Rmay be a key target for selection acting on plumage colour. The pattern of selection atMC1Rseems to be consistent with the continuous or cyclical evolution of traits and preferences that is the outcome of several Fisherian and good-genes models of sexual selection. In contrast, we found no support for models of sexual selection that predict an increase in purifying selection as a result of purging of deleterious mutations or for models that predict an increased rate of mutation in association with stronger sexual selection.
Applications of an amorphous silicon-based area detector for high-resolution, high-sensitivity and fast time-resolved pair distribution function measurements
Authors: Chupas Peter J. , Chapman Karena W. , Lee Peter L.
Published: May 2007

The application of a large-area (41 × 41 cm, 2048 × 2048 or 1024 × 1024 pixel) high-sensitivity (detective quantum efficiency > 65%) fast-readout (up to 7.5 or 30 Hz) flat-panel detector based on an amorphous silicon array system to the collection of high-energy X-ray scattering data for quantitative pair distribution function (PDF) analysis is evaluated and discussed. Data were collected over a range of exposure times (0.13 s–7 min) for benchmark PDF samples: crystalline nickel metal and amorphous silica (SiO2). The high real-space resolution of the resultant PDFs (withQmaxup to ∼40 Å−1) and the high quality of fits to data [RNi(0.13s)= 10.5%,RNi(1.3s)= 6.3%] obtained in short measurement times indicate that this detector is well suited to studies of materials disorder. Further applications of the detector to locate weakly scattering H2molecules within the porous Prussian blue system, {\rm Mn}^{\rm II}_{\,3}[CoIII(CN)6]2·xH2, and to follow thein situreduction of PtIVO2to Pt0at 30 Hz, confirm the high sensitivity of the detector and demonstrate a new potential for fast time-resolved studies.
Improving the quality of diamond anvil cell data collected on an area detector by shading individual diamond overlaps
Authors: Casati N. , Macchi P. , Sironi A.
Published: May 2007

Crystallographic data collected on a CCD using a diamond anvil cell may present overlapping diamond and sample reflections. These false intensities may not be rejected by common data processing programs and may affect the finalhkllist. A utility was developed that shades these reflections during the integration, enabling their elimination before the solution or refinement. Moreover, this procedure avoids the error propagation to other reflections, caused by overlapping spots, through the profile fitting procedure of an integration run.
Two-dimensional small-angle X-ray scattering of self-assembled nanocomposite films with oriented arrays of spheres: determination of lattice type, preferred orientation, deformation and imperfection
Authors: Ruland Wilhelm , Smarsly Bernd M.
Published: May 2007

Mesostructured oxide films were prepared by dip-coating from colloidal solutions on ultrathin Si wafers and solidified by heating at various temperatures. Two-dimensional small-angle X-ray scattering measurements were carried out in transmission under selected tilt angles and evaluated by comparison with analytical expressions. The films are composed of oriented mesophases, the structures of which are defined in terms of lattice type, preferred orientation, deformation and imperfection, notably stacking faults.
Visrock: a program for digital topography and X-ray microdiffraction imaging
Authors: Lübbert Daniel , Baumbach Tilo
Published: May 2007

Visrockis a program for interactive analysis of sequences of digital X-ray images.Visrockwas developed in the context of the rocking-curve imaging method of full-field X-ray microdiffraction imaging. Its functionality is based on parallel profile analysis of millions of local diffraction profiles. Options for subsequent visualization of the spatial distribution of extracted parameters include automatic contrast enhancement, noise reduction and multi-peak analysis. In addition to microdiffraction imaging, further useful applications of the program lie particularly in computed tomography, sequential radiography and analyser-based imaging.
Low-background single-crystal silicon sample holders for neutron powder diffraction
Authors: Potter M. , Fritzsche H. , Ryan D. H. , Cranswick L. M. D.
Published: May 2007

Neutron diffraction measurements on weakly scattering or highly absorbing samples may demand custom mounting solutions. Two low-background sample holders based on inexpensive single-crystal silicon are described. One uses a conventional cylindrical geometry and is optimized for weakly scattering materials, while the other has a large-area flat-plate geometry and is designed for use with highly absorbing samples. Both holders yield much lower backgrounds than more conventional null-matrix or null-scattering materials and are essentially free from interfering Bragg peaks.
Guiding hard X-rays by means of a periodic multilayer waveguide with an air clearance: a numerical study
Authors: Prudnikov I. R.
Published: May 2007

A periodic multilayer waveguide for X-rays with an air gap serving as a guiding layer is considered. The propagation of hard X-ray guided modes through such a waveguide has been investigated with the help of numerical modeling. The propagation lengths of the guided modes are analyzed thoroughly with respect to their dependence on the reflectivity of the periodic multilayers forming the waveguide. It is shown that the guided modes can be generated even in a waveguide composed of low-reflectivity multilayers. The influence of a standing wave inside the reflecting multilayers on the transmission of the guided waves by the waveguide is demonstrated. Conditions which are favorable for the excitation of the guided modes are discussed.
Si(511) channel cut for monochromatization and linear polarization of X-rays
Authors: Stöcker Hartmut , Reuter Katrin K. , Meyer Dirk C.
Published: May 2007

The capabilities of an Si(511) channel-cut monochromator used with an X-ray tube with copper anode are presented. By passing this Si(511) channel-cut crystal, X-rays become both monochromatic and linearly polarized. The monochromaticity of the resulting beam is proved by angular dispersive measurements. Elastic scattering was used to characterize the degree of linear polarization.
On the polyhedral volume ratios VA
/VB
in perovskites ABX
3
Authors: Avdeev Maxim , Caspi El'ad N. , Yakovlev Sergey
Published: May 2007

This paper presents analytical expressions for the calculation of ratios of cation coordination polyhedra volumes (VA
/VB
) for perovskites ABX
3 of the Stokes–Howard diagram directly from atomic coordinates. We show the advantages of quantifying perovskite structure distortion with polyhedral volume ratios rather than with tilting angles, and discuss why space groups with multiple crystallographically inequivalent A or B sites (I4/mmm, Immm, P42/nmc
etc.) are much less common than those with a single A and B site (I4/mcm, R\bar 3c, Pnma
etc.). Analysis of crystallographic data for approximately 1300 perovskite structures of oxides, halides and chalcogenides from the Inorganic Crystal Structure Database revealed that the most highly distorted perovskites belong to the space group Pnma and formally lower-symmetry perovskites (I2/m, I2/a) are less distorted geometrically. Critical values of the VA
/VB
ratios for the most common phase transitions Pnma ↔ I4/mcm and Pnma↔ R\bar 3c are estimated to be ∼ 4.85 with the possible intermediate space group Imma stable in the very narrow range of VA
/VB
≃ 4.8–4.9. Transitions to post-perovskite CaIrO3-type structures may be expected for VA
/VB
< 3.8.
Ab initio structure determination of 5-anilinomethylene-2,2-dimethyl-1,3-dioxane-4,6-dione from laboratory powder data – a combined use of X-ray, molecular and solid-state DFT study
Authors: Smrčok Ľubomír , Jorík Vladimír , Scholtzová Eva , Milata Viktor
Published: May 2007

The crystal structure of the title compound was solved from laboratory powder diffraction data in the triclinic group P\bar 1 by simulated annealing using the program DASH. Since Rietveld refinements yielded inaccurate geometries the structure was finally refined by geometry optimization using energy minimization in the solid state with the DFT/plane-waves approach. The molecule is essentially planar and its Meldrum's acid moiety (2,2-dimethyl-1,3-dioxane-4,6-dione) has a flattened boat conformation. The bond orders in the molecule estimated using a natural bond-orbitals formalism correlate with the optimized bond lengths. The structure in the solid state is based on dimer units in which the molecules are held by N—H...O and C—H...O hydrogen bonds in addition to electrostatic interactions. These units interact through weak C—H...O hydrogen bonds. It is suggested that structure refinement by energy minimization at the DFT level of theory may in many cases successfully replace Rietveld refinement.
Structural similarities in tetraaryltins described by virtual non-crystallographic rotations or translations: Kitaigorodskii's morphotropism is revisited
Authors: Kálmán Alajos , Fábián László
Published: May 2007

Recently Kálmán [(2005), Acta Cryst. B61, 536–547] revealed that semirigid molecules or their patterns held together e.g. by hydrogen bonds may perform non-crystallographic rotations (through 180, 90° etc.) around themselves whenever a substitution, ring enlargement or isomerization destroys the existing close packing, i.e. the novel substituent or the enlarged ring can no longer fit in the hollows formed between the molecules. In other words, the old and new arrangements of such chemically similar molecules can be converted into each other by virtual rotations. However, when a semirigid molecule without substitution, but under the influence of solvents, temperature etc., is fully or partly rearranged in the solid state, the corresponding non-crystallographic rotation (hereinafter ncr) is real and gives rise to polymorphism. Such polymorphs are hallmarked by full or partial isostructurality and show that ncrs always occur together with isostructurality. First Kitaigorodskii [(1961), Organic Chemical Crystallography, New York: Consultants Bureau] reported on the structural similarity of three tetraaryltins, (p-RC6H4)4Sn, R = H, CH3, CH3O, which is terminated by the larger C2H5O group. A revisit to these structures revealed that the tetragonal → monoclinic conversion termed by Kitaigorodskii as a `morphotropic step' is also performed by an ncr. Similarly, other tetraaryltins in the literature are related by ncrs or the nc translation of the semirigid tetrahedra, or they remain isostructural. Since one of the definitions of morphotropism, a word of Greek origin, is `turn of form', the ncrs of semirigid molecules can be denoted – following Kitaigorodskii – by this word, whereas its alternative definition in the morphological crystallography of `unidirectional changes' [applied by Groth (1870). Ber. Chem. Ges.
3, 449–457] covers the non-crystallographic translations described first in this work.
X-ray studies of crystalline complexes involving amino acids and peptides. XLIV. Invariant features of supramolecular association and chiral effects in the complexes of arginine and lysine with tartaric acid
Authors: Selvaraj M. , Thamotharan S. , Roy Siddhartha , Vijayan M.
Published: May 2007

The tartaric acid complexes with arginine and lysine exhibit two stoichiometries depending upon the ionization state of the anion. The structures reported here are DL-argininium DL-hydrogen tartrate, bis(L-argininium) L-tartrate, bis(DL-lysinium) DL-tartrate monohydrate, L-lysinium D-hydrogen tartrate and L-lysinium L-hydrogen tartrate. During crystallization, L-lysine preferentially interacts with D-tartaric acid to form a complex when DL-tartaric acid is used in the experiment. The anions and the cations aggregate into separate alternating layers in four of the five complexes. In bis(L-argininium) L-tartrate, the amino acid layers are interconnected by individual tartrate ions which do not interact among themselves. The aggregation of argininium ions in the DL- and the L-arginine complexes is remarkably similar, which is in turn similar to those observed in other dicarboxylic acid complexes of arginine. Thus, argininium ions have a tendency to assume similar patterns of aggregation, which are largely unaffected by a change in the chemistry of partner molecules such as the introduction of hydroxyl groups or a change in chirality or stoichiometry. On the contrary, the lysinium ions exhibit fundamentally different aggregation patterns in the DL–DL complexes on the one hand and L–D and L–L complexes on the other. Interestingly, the pattern in the L–D complex is similar to that in the L–L complex. The lysinium ions in the DL–DL complex exhibit an aggregation pattern similar to those observed in the DL-lysine complexes involving other dicarboxylic acids. Thus, the effect of change in the chirality of a subset of the component complexes could be profound or marginal, in an unpredictable manner. The relevant crystal structures appear to indicate that the preference of L-lysine for D-tartaric acid is perhaps caused by chiral discrimination resulting from the amplification of a small energy difference.
Redetermination, invariom-model and multipole refinement of L-ornithine hydrochloride
Authors: Dittrich B. , Munshi P. , Spackman M. A.
Published: May 2007

The structure of L-ornithine hydrochloride, C5H13N2O_2^+Cl−, has been redetermined at 100 K by single-crystal X-ray diffraction within a project that aims to generate accurate bond-distance restraints for the invariom refinement of proteins. The high-resolution data were subject to an invariom and a multipole refinement, and the resulting electron densities on a grid were compared. Improvements in the conventional R factor obtained by multipole modelling were smaller than in other structures containing solely the elements CHNO owing to Cl core scattering. Cruickshank's diffraction-component precision index and Stevens & Coppens suitability factor are discussed.