bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing the design of clinical trials where the outcome is a rate. Can estimating a baseline rate in a run‐in period increase efficiency?
Authors: Frost Chris , Kenward Michael G. , Fox Nick C.
Published: May 2008

It is well known that the statistical power of randomized controlled trials with a continuous outcome can be increased by using a pre‐randomization baseline measure of the outcome variable as a covariate in the analysis. For a trial where the outcome measure is a rate, for example in a therapeutic trial in Alzheimer's disease, the relevant covariate is a pre‐randomization measure of that rate. Obtaining this requires separating the total follow‐up period into two periods. In the first ‘run‐in’ period all patients would be ‘off‐treatment’ to facilitate the calculation of baseline atrophy rates. In the second ‘on‐treatment’ period half of the patients, selected at random, would be switched onto active treatment with the others remaining off treatment. In this paper we use linear mixed models to establish a methodological framework that is then used to assess the extent to which such designs can increase statistical power. We illustrate our methodology with two examples. The first is a design with three evenly spaced time points analysed with a standard random slopes model. The second is a model for repeated ‘direct’ measures of changes used for the analysis of imaging studies with visits at multiple time points. We show that run‐in designs can materially reduce sample size provided that true between‐subject variability in rates is large relative to measurement error. Copyright © 2008 John Wiley & Sons, Ltd.
A note on tree gatekeeping procedures in clinical trials
Authors: Dmitrienko Alex , Tamhane Ajit C. , Liu Lingyun , Wiens Brian L.
Published: May 2008

Dmitrienko et al. (Statist. Med. 2007; 26:2465–2478) proposed a tree gatekeeping procedure for testing logically related hypotheses in hierarchically ordered families, which uses weighted Bonferroni tests for all intersection hypotheses in a closure method by Marcus et al. (Biometrika 1976; 63:655–660). An algorithm was given to assign weights to the hypotheses for every intersection. The purpose of this note is to show that any weight assignment algorithm that satisfies a set of sufficient conditions can be used in this procedure to guarantee gatekeeping and independence properties. The algorithm used in Dmitrienko et al. (Statist. Med. 2007; 26:2465–2478) may fail to meet one of the conditions, namely monotonicity of weights, which may cause it to violate the gatekeeping property. An example is given to illustrate this phenomenon. A modification of the algorithm is shown to rectify this problem. Copyright © 2008 John Wiley & Sons, Ltd.
Applicability of MiniPal 4 compact EDXRF spectrometer for soil and sediment analysis
Authors: Oreščanin Višnja , Mikelić Ivanka Lovrenčić , Mikelić Luka , Lulić Stipe
Published: May 2008

Optimum measurement parameters for analysis of soil and sediment samples with the compact MiniPal 4 (MP4)EDXRF spectrometer (PANalytical, Almelo, The Netherlands) were presented. The following elements were considered: K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As and Pb. Since the elements from low Z to medium Z region were covered, three measurement conditions (sequences) were defined. The following parameters were selected for measurement of the elements K, Ti, and V: voltage = 12 kV; current = 750 µA; filter material: Al_thin. Cr, Mn and Fe were measured at 20 kV; 300 µA with Al filter while for measurements of Ni, Cu, Zn, As, Pb, Rb, and Sr an Ag filter was selected and tube voltage and current were 30 kV and 300 µA. Each sequence was measured for 200 s and measurements were done in the air. MP4 spectrometer was characterized with acceptable precision, long‐term stability and satisfactory minimum detection limit for the analyses of soil and sediment materials. For the elements K, Mn, Fe, and Ti the precision of the analysis was better than 0.5% and for all the other elements better than 5%. Detection limits for sediment samples were 20 ppm for K, 6.1 ppm for Ti, 5.2 for Mn, 4 ppm for Fe, 4.2 ppm for As and less than 2 ppm for all the other elements. These values were significantly lower compared to typical concentrations of the same elements found in unpolluted soil and sediments. Copyright © 2008 John Wiley & Sons, Ltd.
X‐ray spectrometry: a powerful tool for the measurement of complete fusion of weakly bound nuclei
Authors: Gomes P. R. S. , Padron I. , Capurro O. A. , Niello J. O. Fernández , Martí G. V. , Pacheco A. J. , Arazi A. , Lubian J. , Crema E.
Published: May 2008

We describe how the method of detection of delayed K x‐rays produced by the electron capture decay of the residual nuclei can be a powerful tool in the investigation of the effect of the breakup process on the complete fusion (CF) cross‐section of weakly bound nuclei at energies close to the Coulomb barrier. This is presently one of the most interesting subjects under investigation in the field of low‐energy nuclear reactions, and the difficult experimental task of separating CF from the incomplete fusion (ICF) of one of the breakup fragments can be achieved by the x‐ray spectrometry method. We present results for the fusion of the 9Be + 144Sm system. Copyright © 2008 John Wiley & Sons, Ltd.
Early Elevation of Intra‐Abdominal Pressure After Laparotomy for Secondary Peritonitis: A Predictor of Relaparotomy?
Authors: Basu Adhish , Pai Dinker R.
Published: May 2008

Background

Patients with secondary peritonitis often require relaparotomy; however, there is no consensus about the criteria for selecting patients who would benefit from early relaparotomy. Our goal was to evaluate whether elevated intra‐abdominal pressure (IAP) during the early postoperative period could predict the need for relaparotomy.

Methods

A total of 102 consecutive adult patients with acute intra‐abdominal conditions were admitted for laparotomy. Seventy‐eight patients, who were diagnosed with secondary peritonitis at index surgery, underwent serial measurements of IAP. The primary outcomes measured in the study were incidence of postoperative peritonitis and mortality.

Results

Thirty‐two of 78 patients with secondary peritonitis (41%) developed elevated IAP postoperatively. Sixteen (20.5%) of 78 patients developed postoperative peritonitis. Twelve of these 16 patients (75%) with postoperative peritonitis had significantly elevated IAP (P = 0.002) during the immediate postoperative period. Regression analysis revealed elevated IAP (P = 0.055) to be third most predictive of postoperative peritonitis in patients who underwent laparotomy for secondary peritonitis, after septic shock at admission (P = 0.012) and POSSUM score (P = 0.018).

Conclusion

Our study shows that development of elevated IAP during the early postoperative period can increase the risk of postoperative peritonitis. IAP measured during the immediate postoperative period can be used as a predictor of early relaparotomy.
From Hell to Paradise? Voluntary Transfer of Convicts to the Andaman Islands, 1921–1940
Authors: SHERMAN TAYLOR C.
Published: May 2008

The paper attempts to understand the challenges and opportunities which the penal settlement at Port Blair in the Andaman Islands presented to colonial governments in twentieth-century India. To this end, the paper examines a scheme drawn up in the 1920s which saw the introduction of a much more liberal regime for convicts in Port Blair. Under these plans, convicts were granted access to land and encouraged to bring their families from the mainland. This research reveals that the policies which determined the history of the settlement in this period were defined by two tensions. First, there was a constant battle between the central authorities and provincial governments over the shape and purposes of the settlement. Second, there was a contradiction between the penal objectives of the colony and the larger strategies which aimed to develop the islands for the greater British empire.
Tracial Rokhlin property for automorphisms on simple -algebras
Authors: LIN HUAXIN , OSAKA HIROYUKI
Published: May 2008

LetAbe a unital simple$A\mathbb {T}$-algebra of real rank zero. Given an isomorphismγ1:K1(A)→K1(A), we show that there is an automorphismα:A→Asuch thatα*1=γ1andαhas the tracial Rokhlin property. Consequently, the crossed product$A\rtimes _{\alpha }\mathbb {Z}$is a simple unital AH-algebra with real rank zero. We also show that automorphisms with the Rokhlin property can be constructed from minimal homeomorphisms on a connected compact metric space.
Singular perturbation of symbolic dynamics via thermodynamic formalism
Authors: MORITA TAKEHIKO , TANAKA HARUYOSHI
Published: May 2008

We consider singular perturbation of a mixing subshift of finite type by means of thermodynamic formalism. In our formulation, the perturbed systems are described by a family of potentials {Φ(α,⋅)} with large parameter α on a fixed subshift of finite type, and the original (unperturbed) system is characterized as the system at infinity obtained by collapsing the perturbed system upon taking $\alpha \to \infty $. We apply our formulation to the collapse of cookie-cutter systems and dispersing open billiards.
High-resolution trends of nutrients, DOM and nitrogen uptake in the annual sea ice at Terra Nova Bay, Ross Sea
Authors: Cozzi Stefano
Published: May 2008

High-resolution trends of nutrients and DOM are analysed, with respect to nitrate and ammonium uptakes, in two coastal stations placed on the annual land-fast ice at Terra Nova Bay. The highest accumulations of dissolved inorganic nitrogen (87.2 µmol N dm-3), reactive phosphorus (14.1 µmol P dm-3) and reactive silicon (22.9 µmol Si dm-3) were observed in the bottom ice, although this process was preceded by a nutrient decrease in an interior sea ice layer. In the upper layer of sea ice, DOM was rather constant in concentration and P-deficient (C:N:P = 377:34:1–579:53:1). In the bottom and platelet ice, the accumulation of DOM (1277 µmol C dm-3; 108.2 µmol N dm-3; 7.67 µmol P dm-3) occurred with lower C:N:P ratios (123:14:1–59:7:1), because of a major contribution of fresher organic matter. Nitrate (< 7.33 µmol N dm-3 d-1) and ammonium (< 2.85 µmol N dm-3 d-1) uptakes in the bottom ice were higher than in the platelet ice. The comparison between the data of N-uptake and the concomitant release of total dissolved nitrogen in the bottom ice indicated that the microbial community may be subjected to low growths in situ and high releases of dissolved nitrogen, when it accumulates in this sea ice habitat.
Viral antibodies in south polar skuas around Davis Station, Antarctica
Authors: Miller Gary D. , Watts Joanne M. , Shellam Geoffrey R.
Published: May 2008

We surveyed south polar skuas (Catharacta maccormickiSaunders) in Antarctica for antibodies to a series of viral agents using blood serum and cloacal swabs from 124 adult skuas. There were no ticks on the subjects and we were unable to isolate virus from any individual. Skuas, however, were seropositive to some avian viruses: 16.9% (20/118) had antibodies to infectious bursal disease virus and 10.5% (11/105) were seropositive for Newcastle disease. We found 1.0% (1/98) had antibodies to avian influenza, no evidence of egg drop syndrome (0/48), but 27.8% (10/36) had antibodies to flaviviruses. Clearly south polar skuas encounter a variety of pathogens either in Antarctica or during their migration in the non-breeding season. There was no evidence of disease in skuas, but the presence of antibodies to pathogens indicates the need to continue to search for the origins of these immunological challenges.
Age, geographical distribution and taphonomy of an unusual occurrence of mummified crabeater seals on James Ross Island, Antarctic Peninsula
Authors: Nelson A.E. , Smellie J.L. , Williams M. , Moreton S.
Published: May 2008

An unusually dense collection of some 150 dead crabeater seals (Family Phocidae), in various stages of decay, occurs in the Brandy Bay hinterland, north-western James Ross Island, northern Antarctic Peninsula. Throughout the past 100 years, the presence of shelf ice (no longer present today) and sea ice in Prince Gustav Channel, between James Ross Island and the Antarctic Peninsula, has prevented seals from readily accessing the western side of James Ross Island. However, open water pools, some over one kilometre in diameter, remain accessible throughout the winter months, allowing seals to haul out onto the ice. It is likely that some of these seals may become disorientated as they wander away from the pools and instead head toward Brandy Bay and onto low-lying and snow-covered Abernethy Flats, easily mistaken for sea ice in early winter, where they perish. The large number of variably-decayed animals present suggests that this has probably happened on numerous occasions. However, some of the dead seals also probably perished during a documented mass dying event of crabeater seals in Prince Gustav Channel caused by an unidentified epidemic, possibly phocine distemper virus (PDV), during the spring of 1955.
Characterization of Cold Spray Titanium Deposits by X-Ray Microscopy and Microtomography
Authors: Zahiri Saden H. , Mayo, Sheridan C. , Jahedi Mahnaz
Published: May 2008

Cold gas dynamic spray (cold spray) is a rapid deposition technology in which particles deposit at velocities above the speed of sound (∼340 ms−1). Generally, porosity forms in cold spray deposits due to insufficient deformation of particles. In this study, the unique capability of the X-ray microscopy and microtomography is utilized to visualize the internal structure of deposited material. The results show that this characterization technique successfully reveals porosities in the cold spray commercial purity (CP) titanium structure. Furthermore, microtomography images confirmed the experimental results for porosity measurements in which helium (compared with nitrogen) as carrier gas significantly decreases porosity in cold spray CP titanium.
Saturation of the polar cap potential: Inference from Alfvén wing arguments
Authors: Kivelson Margaret G. , Ridley Aaron J.
Published: May 2008

The cross polar cap potential varies roughly linearly with the solar wind electric field for nominal conditions but asymptotes to a constant value of order 200 kV for large electric field. When the impedance of the solar wind across open polar cap field lines dominates the impedance of the ionosphere, Alfvén waves incident from the solar wind are partially reflected, reducing the signal in the polar cap. Thus, the ratio of the cross polar cap potential to the potential imposed by the solar wind is 2ΣA/(ΣP + ΣA), where ΣA is the Alfvén conductance of the solar wind (= (ρsw/μo)1/2/Bsw) to within a density‐dependent factor on average of order 1, ΣP is the Pedersen conductance of the ionosphere, and ρsw (Bsw) is the density (magnetic field magnitude) of the solar wind. For small Bsw, the response is proportional to Bsw. For large Bsw, the cross polar cap potential depends only on the solar wind dynamic pressure (with small viscous and density‐dependent corrections). Quantitative estimates require knowledge of ΣP and the dependence of the potential imposed by the solar wind on its measured properties; standard assumptions yield saturation levels consistent with observations made during 13 storm intervals. Previous explanations of saturation have invoked changing reconnection efficiency, specific characteristics of the Region 1 current system, or the effect of the bow shock on the reconnecting plasma. Although our relation is mathematically similar to some previously proposed, our arguments place no constraints on reconnection efficiency or on magnetospheric geometry.
The relationship between j × B and ∇·Pe in the magnetotail plasma sheet: Cluster observations
Authors: Henderson P. D. , Owen C. J. , Lahiff A. D. , Alexeev I. V. , Fazakerley A. N. , Yin L. , Walsh A. P. , Lucek E. , Réme H.
Published: May 2008

In this paper we report an extension to Henderson et al.'s (2006) case study, in which we investigate the generality of the anticorrelation between the ∇·e and j × B terms in Ohm's law observed in the plasma sheet. Further current sheet crossings are investigated which occurred on 17 August 2003 and 24 September 2003. Data from this period are particularly relevant as the interspacecraft separations are at their smallest for the Cluster mission. We confirm the generality of the observed anticorrelation and observe that the contributions to the electric field were mainly in the direction normal to the neutral sheet. A simple magnetohydrostatic treatment is used to explain the correlation and directional organization. The treatment is able to explain the anticorrelation and how the relative contributions to the electric field from the ∇·e and j × B terms in Ohm's law may be linked to the temperature ratio of the different plasma constituents as well as their spatial scales. In the examples reported here, the scale length over which the electron pressure changed le was smaller than the scale over which the ion pressure changed li, with le/li being between ∼0.1 and ∼0.4.
Analysis of plasma waves observed within local plasma injections seen in Saturn's magnetosphere
Authors: Menietti J. D. , Santolik O. , Rymer A. M. , Hospodarsky G. B. , Persoon A. M. , Gurnett D. A. , Coates A. J. , Young D. T.
Published: May 2008

Plasma injections or density depletion regions have been reported to be a prolific feature of Saturn's inner magnetosphere. They are characterized by flux tubes of warm, tenuous plasma in a cooler, locally produced plasma background. The injected plasma undergoes dispersion in energy due to gradient and curvature drifts as the flux tube transports. The plasma waves within these injections are of at least two types. Above the electron cyclotron frequency, fce, very intense and narrow‐banded emissions resembling electrostatic cyclotron harmonics (ECH) are often observed. Below fce, whistler mode chorus is sometimes observed. Inside the plasma injections there exists a low‐energy (<100 eV) electron component which tends to have a field‐aligned pitch angle distribution, and a warmer (E > 1000 eV) component with “pancake” pitch angle distributions (peaked at 90°). We model the electron plasma distributions observed inside one injection to conduct a linear dispersion analysis of the wave modes. The results suggest that the ECH emissions can be generated by phase space density gradients associated with a narrow loss cone that is likely to be present but not observed because the electron detectors field of view did not include the magnetic field line at the time of the observations. The whistler mode chorus emission can be generated by the pancake‐like distribution and temperature anisotropy (T⊥/T∥ > 1) of the warmest plasma population. Some interesting anomalies between the results and the observations may be resolved by analyses of additional injection events.
The 2000 western Tottori (Japan) earthquake: Triggering of the largest aftershock and constraints on the slip‐weakening distance
Authors: Di Carli Sara , Voisin Christophe , Cotton Fabrice , Semmane Fethi
Published: May 2008

We investigate the stress time relationships between a mainshock and its largest aftershock. We focus on the 2000 western Tottori (Japan) earthquake (M6.6–6.8) and on the triggering of its largest aftershock (Ms5.5) that occurred 48 h later. We compute both the static Coulomb stress change and the complete Coulomb failure function that provides the evolution of the stress field on the fault plane of the largest aftershock. We show that the static Coulomb stress change is always negative. Therefore it cannot explain the triggering of the largest aftershock, located in a stress shadow. On the contrary, the complete Coulomb failure function exhibits a large positive pulse because of the rupture dynamics of the mainshock. This is consistent with the triggering of the largest aftershock by transient stresses. In a second step, we infer a lower threshold for the critical slip‐weakening distance. Using a frictional model based on a nonlinear, slip‐dependent friction law and assuming the initial state of stress on the fault plane of the largest aftershock, we derive for the slip‐weakening distanceDca value greater than 0.2 m to be consistent with the observed delay of 48 h.
Impacts of spatial resolutions and data quality on soil moisture data assimilation
Authors: Parada Laura M. , Liang Xu
Published: May 2008

The resolution of near‐surface soil moisture imagery derived from passive remote sensing sources is expected to be on the order of 30 km in the foreseeable future. While analogous active remote sensing retrievals may be derived at finer scales (∼100 m), these have been shown to be prone to error and increased uncertainties in the presence of vegetation and/or dominant surface roughness effects. In this study, we resort to an extension of multiscale Kalman filtering (MKF) for assimilation of near‐surface soil moisture retrievals derived during the Southern Great Plains Hydrology experiment of 1997 (SGP97) into the Three‐Layer Variable Infiltration Capacity (VIC‐3L) land surface model. Our first objective is to evaluate impacts of resolution of the passive remotely sensed soil moisture imagery (from 0.78 km to 25 km) on the consistency of the assimilation algorithm and the effectiveness of assimilation with regards to improving the prediction of soil moisture states and energy fluxes from VIC‐3L. Motivated by recent evidence suggesting that temporal ratios of near‐surface soil moisture retrievals from active remote sensing sources may retain much of the soil moisture signal, we additionally assess the value of synthetically derived fine (0.78 km) scale temporal ratios of near‐surface soil moisture when assimilated in conjunction with coarse (25 km) resolution retrievals of near‐surface soil water content. Temporal ratios of soil moisture may, in general, be thought of as a noisy data set conveying information on the spatial organization of near‐surface soil moisture as opposed to reliable estimates of specific volumetric water content values. We find that the joint assimilation of synthetic temporal ratios of soil moisture and coarse volumetric soil moisture retrievals leads to the recovery of relevant spatial features not captured in the 25‐km data set or by VIC‐3L.
Identification and characterization of dendritic, parallel, pinnate, rectangular, and trellis networks based on deviations from planform self‐similarity
Authors: Mejía Alfonso I. , Niemann Jeffrey D.
Published: May 2008

Geomorphologists have long recognized that the geometry of channel network planforms can vary significantly between regions depending on the local lithologic and tectonic conditions. This tendency has led to the classification of channel networks using terms such as dendritic, parallel, pinnate, rectangular, and trellis. Unfortunately, available classification methods are scale dependent and have little connection to any underlying quantitative theory of drainage network geometry or evolution. In this study, a new method is developed to classify drainage networks on the basis of their deviations from self‐similarity. The planform geometry of dendritic networks is known to be approximately self‐similar. It is our hypothesis that parallel, pinnate, rectangular, and trellis networks correspond to distinct deviations from this self‐similarity. To identify such deviations, three measures of channel networks are applied to 10 networks from each classification. These measures are the incremental accumulation of drainage area along channels, the irregularity of channel courses, and the angles formed by merging channels. The results confirm and characterize the self‐similarity of dendritic networks. Parallel and pinnate networks are found to exhibit anisotropic scaling. Rectangular and trellis networks are approximately self‐similar although deviations from self‐similarity are observed. Rectangular networks have more sinuous channels than dendritic networks across all scales, and trellis networks have a slower rate of area accumulation than dendritic networks across all scales. Such observations are used to build and test simple classification trees, which are found to perform well in classifying networks.
Energy and water additions give rise to simple responses in plant canopy and soil microclimates of a high arctic ecosystem
Authors: Sullivan Patrick F. , Welker Jeffrey M. , Steltzer Heidi , Sletten Ronald S. , Hagedorn Birgit , Arens Seth J. T. , Horwath Jennifer L.
Published: May 2008

Energy and water inputs were increased during the snow‐free season to test the sensitivity of a cold, dry ecosystem to climate change. Infrared radiators were used to provide two levels of supplemental radiation (T1 and T2) to prostrate dwarf‐shrub, herb tundra in northwest Greenland. The higher radiation addition was combined with supplemental water in a factorial design. Radiation additions increased midday canopy temperatures by up to 4.0°C and 6.0°C and growing season mean shallow soil temperatures by 1.3°C and 2.4°C in T1 and T2 plots, respectively. Soil warming was measured at and probably exceeded 10 cm in depth. There was no evidence of soil drying in plots that received additional radiation, in contrast with other studies, nor was there evidence that supplemental water interacted with radiation additions to affect soil temperatures. Water additions were generally undetectable against a background of large seasonal changes in soil water content. We suggest that well‐drained soils and strong seasonal controls on soil water contents (e.g., soil thaw and evapotranspiration) limit the system's sensitivity to changes in precipitation during the brief growing season. In general, multifactor changes in climate gave rise to simple changes in the vegetation microclimate of this cold, dry ecosystem.
Systematic pressure enhancement of titanomagnetite magnetization
Authors: Gilder Stuart A. , Le Goff Maxime
Published: May 2008

A poorly understood facet of magnetism concerns its response to the imposition of very high pressures. Here we show that pressure systematically enhances the magnetic properties of titaniferous oxides (titanomagnetite), which are the principal carriers of magnetic remanence in nature. For example, at 4 GPa, saturation remanent magnetization intensities increase by a factor of 2, 3, 13 and 21 for titanomagnetite with 0, 20, 40 and 60% titanium in the structure, respectively. Magnetic coercivity also dramatically rises with pressure for high Ti species. The magnetization intensities and coercivities remain permanently elevated after pressure release. Pressure thus makes multidomain titanomagnetite more single domain‐like, which can potentially explain deeply rooted magnetic anomalies on Earth and other planets.
Exploiting the potential of an improved multimission altimetric data set over the coastal ocean
Authors: Bouffard J. , Vignudelli S. , Cipollini P. , Menard Y.
Published: May 2008

Until now, most satellite altimetry studies of the coastal ocean have been based on along‐track data from a single mission, whereas up to four missions were operative in 2002–2005. Here, to monitor the coastal ocean we have applied specialized corrections and dedicated processing strategies to compute a multimission data set at a mean distance of 32 km of the coast. The resulting altimetric data set is compared with sea level data from three in situ stations over a coastal zone of the northwestern Mediterranean. The mean rms difference between this data set and the sea level stations is 2.9 cm against 3.7 cm when using the AVISO altimetric product. Comparison of altimeter‐derived geostrophic velocities with a mooring also shows that the spatial and temporal variability of the surface current field is well reproduced. The agreement with in situ measurements extends to intraseasonal time scales showing a significant improvement compared to previous studies in the 50 km coastal‐band.
A reciprocal repression between ZEB1 and members of the miR‐200 family promotes EMT and invasion in cancer cells
Authors: Burk Ulrike , Schubert Jörg , Wellner Ulrich , Schmalhofer Otto , Vincan Elizabeth , Spaderna Simone , Brabletz Thomas
Published: May 2008

The embryonic programme ‘epithelial–mesenchymal transition’ (EMT) is thought to promote malignant tumour progression. The transcriptional repressor zinc‐finger E‐box binding homeobox 1 (ZEB1) is a crucial inducer of EMT in various human tumours, and was recently shown to promote invasion and metastasis of tumour cells. Here, we report that ZEB1 directly suppresses transcription of microRNA‐200 family members miR‐141 and miR‐200c, which strongly activate epithelial differentiation in pancreatic, colorectal and breast cancer cells. Notably, the EMT activators transforming growth factor β2 and ZEB1 are the predominant targets downregulated by these microRNAs. These results indicate that ZEB1 triggers an microRNA‐mediated feedforward loop that stabilizes EMT and promotes invasion of cancer cells. Alternatively, depending on the environmental trigger, this loop might switch and induce epithelial differentiation, and thus explain the strong intratumorous heterogeneity observed in many human cancers.
New infinite-dimensional quadruple symmetry groups for the general symplectic gravity model
Authors: Gao Ya-Jun
Published: May 2008

The symmetry structures of the general symplectic gravity model are further studied. By using the so-called extended double (ED)-complex function method, the usual Riemann–Hilbert (RH) problem is extended to an ED-complex formulation. For any fixed non-negative integer n, two pairs of ED RH transformations are constructed and they are verified to give infinite-dimensional quadruple symmetry groups of the general symplectic gravity model, each of these symmetry groups has the structure of semidirect product of Kac–Moody group Sp(2(n+1̂),R) and Virasoro group. Moreover, the infinitesimal forms of these RH transformations are calculated out and they are found to give exactly the same results as previous; these demonstrate that the two pairs of ED RH transformations in this paper provide exponentiations of all the infinitesimal symmetries in our previous paper. The finite forms of symmetry transformations given in the present paper are more important and useful for theoretic studies and new solution generation, etc.
Magnetization process of lotus-type porous metals
Authors: Onishi H. , Hyun S. K. , Nakajima H. , Mitani S. , Takanashi K. , Yakushiji K.
Published: May 2008

Effects of porosity and pore orientation on the magnetization process were studied for lotus-type porous nickel and cobalt. It was confirmed that the saturation magnetization of porous metals varied linearly with the porosity, independent of the pore growth directions. Anisotropic behavior was clearly observed for the magnetization curves of lotus-type porous nickel, i.e., the magnetization perpendicular to the pore growth direction is always smaller than that parallel to the pore growth direction. The observed anisotropy is significantly large in the low magnetic field range below 2.5kOe and is attributed to the anisotropic forms of the pores. Furthermore, it was found that the porosity dependence of magnetization at a certain applied field can be expressed by the empirical formula called Archie’s law, and the values of their exponents in the parallel and perpendicular directions at around 200Oe were determined to be 1.1 and 1.8, respectively. These values are coincident with those reported for electrical conductivity of lotus-type porous nickel in the parallel and perpendicular directions.
Eckart axis conditions, Gauss’ principle of least constraint, and the optimal superposition of molecular structures
Authors: Kneller Gerald R.
Published: May 2008

The relation of the Eckart axis conditions for polyatomic vibrating molecules to the problem of optimal superposition of molecular structures has been pointed out recently [J. Chem. Phys. 122, 224105 (2005)]. Here, it is shown that both problems are intimately related to Gauss’ principle of least constraint, for which a concise derivation is presented. In the context of this article, Gauss’ principle leads to a rotational superposition problem of the unconstrained atomic displacements and the corresponding displacements due to a molecular rigid-body motion. The Eckart axis conditions appear here as necessary conditions for a minimum of the constraint function. The importance of Eckart’s problem for extracting the internal motions of macromolecules from simulated molecular dynamics trajectories is pointed out, and it is shown how the case of coarse-grained sampled trajectories can be treated.
Characterization of the sequential product on quantum effects
Authors: Gudder Stan , Latrémolière Frédéric
Published: May 2008

We present a characterization of the standard sequential product of quantum effects. The characterization is in terms of algebraic, continuity and duality conditions that can be physically motivated.
Electronic and magnetic properties of armchair and zigzag graphene nanoribbons
Authors: Owens Frank J.
Published: May 2008

The electronic properties, band gap, and ionization potential of zigzag and armchair graphene nanoribbons are calculated as a function of the number of carbon atoms in the ribbon employing density functional theory at the B3LYP∕6-31G* level. In armchair ribbons, the ionization potential and band gap show a gradual decrease with length. For zigzag ribbons, the dependence of the band gap and ionization potential on ribbon length is different depending on whether the ribbon has an unpaired electron or not. It is also found that boron and nitrogen zigzag and armchair doped graphene nanoribbons have a triplet ground state and could be ferromagnetic.
Single-sweep methods for free energy calculations
Authors: Maragliano Luca , Vanden-Eijnden Eric
Published: May 2008

A simple, efficient, and accurate method is proposed to map multidimensional free energy landscapes. The method combines the temperature-accelerated molecular dynamics (TAMD) proposed in [L. Maragliano and E. Vanden-Eijnden, Chem. Phys. Lett. 426, 168 (2006)] with a variational reconstruction method using radial-basis functions for the representation of the free energy. TAMD is used to rapidly sweep through the important regions of the free energy landscape and to compute the gradient of the free energy locally at points in these regions. The variational method is then used to reconstruct the free energy globally from the mean force at these points. The algorithmic aspects of the single-sweep method are explained in detail, and the method is tested on simple examples and used to compute the free energy of the solvated alanine dipeptide in two and four dihedral angles.
Quantitative imaging of Young’s modulus of solids: A contact-mechanics study
Authors: Ogi H. , Inoue T. , Nagai H. , Hirao M.
Published: May 2008

We developed equipment and methods for measuring quantitatively the local Young’s modulus of solids. It consists of an electrodeless langasite oscillator and line antennas, and oscillator vibrations are generated and detected contactlessly. A constant biasing force results from oscillator mass and is independent of surface roughness. The effect of material anisotropy on the measured stiffness is theoretically discussed for studying the limitation of the quantitative measurement. The microscopy has been applied to polycrystalline copper, and the measured modulus is compared to calculations based on electron-backscatter-diffraction measurements. Also, we applied it to a duplex stainless steel and an embedded silicon-carbide fiber. The results reveal textured regions, defects with high sensitivity, and even stiffness distribution in a single grain.
Quantum-limited mass flow of liquid He3
Authors: Lambert G. , Gervais G. , Mullin W. J.
Published: May 2008

We consider theoretically the possibility of observing unusual quantum fluid behavior in liquid He3 and solutions of He3 in He4 systems confined to nanochannels. In the case of pure ballistic flow at very low temperature the conductance will be quantized in units of 2m2∕h. We show that these steps should be sensitive to increases in temperature. We also use a random scattering matrix simulation to study flow with diffusive wall scattering. Universal conductance fluctuations analogous to those seen in electron systems should then be observable. Finally we consider the possibility of crossover to a one-dimensional system at sufficiently low temperature, where the system could form a Luttinger liquid.
On cavitation in liquid helium in a flow due to a vibrating quartz fork
Authors: Blažková M. , Schmoranzer D. , Skrbek L.
Published: May 2008

Cavitation in normal and superfluid liquid He4 at saturated vapor pressure and slightly elevated pressures has been experimentally studied in a flow due to quartz forks vibrating at high amplitudes. Above the temperature- and pressure-dependent critical velocity, heterogeneous cavitation is observed both visually and electrically, as a breakdown of the resonance response of the fork. We compare our results with available experimental and discuss them using existing theoretical models. In particular, we show that thermal effects leading to local overheating of the vicinity of the fork have to be taken into account, especially in normal liquid He4.
Bubble nucleation in a superfluid He3–He4 mixture induced by acoustic wave
Authors: Abe H. , Saitoh Y. , Ueda T. , Nomura R. , Okuda Y. , Burmistrov S. N.
Published: May 2008

The nucleation dynamics of bubbles induced by an acoustic wave pulse in He3–He4 liquid mixtures is reported. The experiment is performed mixtures with fixed He3 concentrations of about 4% and 25% and for pure superfluid He4. When a pulse of 1ms duration is applied to the mixture at the saturated vapor pressure, a spherical bubble is nucleated on the active area of a piezoelectric transducer. For the case of pure He4 it is not a spherically shaped bubble but an irregularly shaped, larger one that is observed. Pictures of the bubble expansion and contraction motions after the nucleation are taken with a high speed CCD camera. The temperature dependence of the bubble nucleation is also investigated by changing the acoustic wave power. The results show that the nucleation and growth dynamics of a cavitation bubble depend greatly on the He3 concentration and temperature.
Observation of acoustic turbulence in a system of nonlinear second sound waves in superfluid He4
Authors: Ganshin A. N. , McClintock P. V. E. , Efimov V. B. , Kolmakov G. V. , Mezhov-Deglin L. P.
Published: May 2008

The results of recent studies of acoustic turbulence in a system of nonlinear second sound waves in a high-quality resonator filled with superfluid He4 are discussed. It is found that when the driving amplitude is increased sufficiently, a steady-state direct wave cascade, involving a flux of energy towards high frequencies, is formed. The wave amplitude distribution follows a power law over a wide range of frequencies. Development of a decay instability at high driving amplitudes results in the formation of subharmonics of the driving frequency, and to a backflow of energy towards the low-frequency spectral domain, in addition to the direct cascade.
Energy spectrum of the velocity field induced by a fractal vortex line in superfluid helium
Authors: Nemirovskiĭ S. K. , Andryushchenko V. A.
Published: May 2008

A Gaussian model of a vortex tangle is used to calculate the energy spectrum E(k) of a three-dimensional random velocity field induced by chaotic vortex lines. It is proposed that the lines have a random-walk structure (Brownian line) with different Hausdorff dimension HD. It is shown that for a fractal vortex line characterized by HD the energy spectrum has the form E(k)∼kHD−2 for large k and the universal form E(k)∼k2 for small k. The characteristics at short distances from a vortex line are similar to a smooth line.
Diatomic model of a quantum crystal
Authors: Poluéktov Yu. M.
Published: May 2008

The anharmonic zero-point vibrations of a crystal are studied using a two-atom model. It is shown that the amplitude of such vibrations cannot exceed a certain limiting value, which is a fraction of the interatomic distance. Compressing the crystal decreases and stretching increases the amplitude of the zero-point vibrations. It is found that the melting temperature of the crystal depends on the de Boer parameter, which is qualitatively close to the observed dependence. It is shown that the melting temperature satisfies Lindemann’s formula in the classical limit. There exists a critical value of the de Boer parameter for which the melting temperature vanishes. For values of the de Boer parameter less than but close to the critical value, melting is of a strongly quantum character.
Dip-effect in the conductivity of 2D electrons on a helium film with a rough substrate
Authors: Leiderer P. , Nazin S. , Shikin V.
Published: May 2008

The phenomenon generally referred to as the dip-effect in the conductivity of 2D electrons on a helium film with a rough substrate is discussed. The particular case where this effect arises with the motion of 2D electrons along a helium film on a periodically corrugated substrate is examined. Arguments for and against the use of this scenario for 2D electrons on arbitrary rough surfaces are presented.
Interaction of microwaves with superfluid flow in HeII
Authors: Rybalko A. S. , Rubets S. P. , Rudavskiĭ É. Ya. , Tikhiĭ V. A. , Golovashchenko R. , Derkach V. N. , Tarapov S. I.
Published: May 2008

The absorption of 40–200GHz electromagnetic waves in liquid helium at temperatures 1.4–2.8K is investigated experimentally. The spectrum of oscillations of the “whispering gallery” modes of a dielectric disk-shaped resonator immersed in liquid helium is recorded. Superfluid flows in HeII is produced artificially using two “heat guns.” A narrow microwave absorption line has been detected at a frequency corresponding to the excitation energy of a single roton. It has been determined that the character of the resonance line changes radically as the velocity vs of the superfluid flow increases: microwave absorption was replaced by induced microwave emission, which was seen as a sharp intensification of the high frequency signal. The effect can be explained qualitatively on the basis of a two-level model of HeII. An abrupt change in the velocity of the superfluid flow is observed with continual increase of the power delivered to the heat gun. This could attest to quantization of vs. It is shown that the superfluid flow has a low-frequency effect on a microwave which outwardly is manifested as modulation of microwave oscillations. Possible reasons for this effect are analyzed.
On the possible nature of the electric activity of HeII
Authors: Loktev V. M. , Tomchenko M. D.
Published: May 2008

An attempt is made to explain the nature of the electric signals observed in helium II in a second-sound standing wave. It is shown on the basis of the general principles of quantum mechanics that as a result of interatomic interactions each helium atom acquires a small induced dipole moment dat, which pulsates in time and space. A directed flux of microscopic vortex rings is formed in a second-sound standing half-wave. This flux partially orders the chaotically oriented dipole moments of the atoms, which results in volume polarization of helium II. The observed potential difference ΔU≈kBΔT∕2e can be explained theoretically by assuming that each ring possesses a dipole moment dvr of the order of 10 times the average value of the modulus of the atomic moment, dvr∼10d¯at. Analysis taking account of the boundary conditions also shows that a different possible nature of the observed electric signal ΔU is also not ruled out: this signal is associated not with the properties of HeII but rather with a form of the thermal electromotive force.
Formation of a glass phase in solid He4. Contribution to the pressure in the supersolid region
Authors: Grigor’ev V. N. , Maĭdanov V. A. , Rubanskiĭ V. Yu. , Rubets S. P. , Rudavskiĭ É. Ya. , Rybalko A. S. , Tikhiĭ V. A.
Published: May 2008

High-precision barometry is used to perform measurements of the temperature dependence of the pressure of helium crystals, located in a constant volume, in the temperature range 50–800mK on crystals of different quality ranging from freshly prepared to carefully annealed. It is found that an additional contribution to the pressure, proportional to T2, appears in on annealed samples. This contribution becomes dominant at T<300mK, i.e. the region where anomalous behavior of solid helium, ascribed to the super solid effect, was previously observed. Such behavior of the pressure is characteristic for the glass phase, and this phase was practically absent in carefully annealed samples. The observed effect shows that in solid helium containing a high concentration of nonequilibrium defects a glass phase forms easily on cooling. Anomalously high pressure relaxation in low-quality samples was also detected in the experiments at temperatures close to the melting temperature. The possible reasons for this effect are discussed.
Electron attachment to atomic hydrogen on the surface of liquid He4
Authors: Arai T. , Yayama H. , Kono K.
Published: May 2008

We demonstrate a possibility that helium surface electrons at cryogenic temperatures can be used as a new source of very low energy electrons. Since both electrons (e−) and hydrogen atoms (H) are bound on liquid helium surface, two-dimensional mixture gas of these two species is available on the surface. We found that low energy collision of e− and H drives electron attachment to form a negative hydrogen ion (H−) in the mixture. From our temperature dependence measurement of the reaction rate, it was found that another H atom participate in the reaction. Namely, the reaction is expressed as H+H+e−→H−+H. Possible reaction mechanisms are discussed in terms of direct three-body process and dissociative attachment process. Measurements in applied magnetic field (B) show that the reaction rate coefficient is suppressed as ∼B−2. This implies that electron spin singlet collision is relevant for electron attachment.
A completely self-contained cryogen-free dilution refrigerator, the TritonDRTM
Authors: Mikheev V. A. , Noonan P. G. , Adams A. J. , Bateman R. W. , Foster T. J.
Published: May 2008

Oxford Instruments have developed a new dilution refrigerator for ultralow temperatures down to below 35mK. The TritonDRTM system is a continuous cryogenic cycle dilution refrigerator. The refrigerator is driven by a closed cycle cryocooler and hence requires no liquid cryogens. The system has a dedicated electronic control unit and software that provides full control of operation.