bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic transport time through mesoscopic devices with contact barriers
Authors: Altland Alexander 
Published: May 2007

AbstractInformation about the transport time of electrons through a quasi one‐dimensional sample is obtained by calculating the energy auto‐correlation function of the conductance. Depending on the length of the sample and its coupling to the external device (here modelled by perfectly conducting leads), the transport time undergoes a smooth crossover between two different limiting regimes. In the case of long samples and good coupling it coincides with the diffusion time. In the opposite limit of short and weakly coupled systems, however, the transport time is given by the reciprocal of the quantum mechanical decay width into the leads. The transition between both regimes is discussed in terms of a few model independent concepts.
Dirac particle, gravity, and inertial effects
Authors: Huang Justin C. 
Published: May 2007

AbstractDirac's equation with gravity for a noninertial observer is derived using local coordinate methods. Calculations for the equation are carried out to second order in the local coordinates. For easy application to interference experiments, the Schrödinger form of the Dirac equation with a well defined Hamiltonian in the local coordinates is presented. The presence of gravitational weighting factors in the scalar product lead to hermitian and antihermitian sectors for the Hamiltonian. The antihermitian part depends directly on the curvature and vanishes for zero curvature. The hermitian part which is important for the determination of phases is studied in detail and the nonrelativistic case is obtained by the application of three successive Foldy‐Wouthuysen transformations. The results also give local currents and interactions which have pure inertial, pure gravity and mixed sectors. The pure inertial terms are the ones obtained by Hehl and Ni. The pure gravity and mixed sectors have contributions which are electric, magnetic and double magnetic in character. The focus is on the curvature contributions. Some are well within reach of the anticipated accuracy of atomic interferometers currently under consideration and other terms may follow if improvements can be made.
Influence of the Ca:Pb ratio on the superconducting properties of Bi‐based ceramics of type 2223
Authors: Rentschler T. , Schulz C. , Zoller P. , Lösch S. , Raff E. , Wischert W. , Kemmler‐Sack S. , Kessler P. , Lichte H. , Nissel T. , Huebener R. P. 
Published: May 2007

AbstractFrom a study of the influence of the Ca: Pb ratio on the superconducting properties of Bibased ceramics of 2223 type it follows that as a second parameter the employed gas atmosphere must be taken into consideration. In case of air preparation good intragrain and intergrain properties are obtained for Ca rich samples (e.g. Bi1.8Pb0.2Sr1.9Ca2.1 Cu3Oz); whereas for Pb rich materials (e.g. Bi1.7Pb0.5Sr1.9Ca1.9 Cu3Oz) improved conditions are encountered by employment of an Ar/O2 (8%) atmosphere during synthesis. Independently, the transition temperature is situated near 108 K.
Bound states and superfluidity in strongly coupled Fermion systems
Authors: Röpke G. 
Published: May 2007

AbstractThe crossover from Bardeen‐Cooper‐Schrieffer pairing to Bose‐Einstein condensation is considered with special emphasis to a consistent description of bound pair formation. A nonequilibrium approach is considered, and wave equations for the two‐particle states and the pair amplitude are derived in the stationary state. The critical temperature is calculated for a simple model system.
Noises generated by nonlinear autoregression
Authors: Kumičák J. 
Published: May 2007

AbstractA nonlinear generalization of autoregressive scheme of first order is suggested as approximate model for 1/fk noises. The iterative generation makes use of reducing function instead of a constant. Computer simulations – carried out over three decades of frequency – have demonstrated that there is such a family of these functions that to any function of the family there exists a unique value of standard deviation of white noise source such that the noise generated by the iterative scheme has the spectral factor k ≈ 1.Implications of the results for understanding the origin, structural stability and ubiquity of 1/f noise are discussed.
Low frequency acoustic and dielectric measurements on glasses
Authors: Classen J. , Enss C. , Bechinger C. , Weiss G. , Hunklinger S. 
Published: May 2007

AbstractThe acoustic and dielectric properties of different glasses at audio frequencies and temperatures below 1 K have been investigated with the vibrating reed and a capacitance bridge technique. We found the temperature dependence of the absorption of vitreous silica (Suprasil W) to agree with the predictions of the tunneling model which is commonly used to explain the low temperature behaviour of amorphous materials. The variation of the sound velocity and of the dielectric constant, however, shows significant deviations from the expected behaviour which cannot be accounted for by a simple modification of the model. Instead, it seems to be necessary to introduce a temperature dependence of some relevant model parameters. Moreover, at very low temperatures (T < 0.1 K) the sound velocity strongly depends on the excitation levels. The absence of this effect at higher temperatures proves that it can be ascribed to a nonlinear response of tunneling systems. Similar results were found in sound velocity measurements on a cover glass and on a superconducting metallic glass (Pd30Zr70, Tc = 2.6 K), which indicates that these features are a general aspect of the dynamics of tunneling states in glasses. In contrast to the insulating glasses we found that in Pd30Zr70 also the internal friction is strain dependent.
Investigation of positively charged acceptor states in Si and Ge under uniaxial stress by phonon induced conduction
Authors: Groß P. , Laßmann K. 
Published: May 2007

AbstractWe use superconducting Al‐tunnel junctions as tunable phonon generators in the meV‐range to determine ground state splitting at zero stress of positively charged states associated with single acceptors in Si and double acceptors in Ge. From the stress and energy dependence of the conductivity induced by high frequency phonon irradiation of the corresponding two‐ and three‐hole states we find that the splitting is below 0.1 meV for the ground states of Si:B+ and Ge:Be+, and 1 meV and 1.2 meV for Si:Ga+ and Si:Al+, respectively. These level separations are comparable to those found previously for the ground states of the corresponding acceptor bound excitons A0X. For the deeper acceptors Si:In+, Si:Tl+, and Ge:Zn+ the results are qualitatively different.
Coherent tunneling of lithium defect pairs in KCl crystals
Authors: Weis R. , Enss C. , Würger A. , Luty F. 
Published: May 2007

AbstractThe tunneling of two lithium ion impurities on next‐nearest neighbor sites in potassium chloride are investigated both experimentally and theoretically. The strong dipolar interaction leads to coherent tunneling motion of the two defect ions between degenerate off‐center positions. Comparing data of rotary echo experiments for impurity pairs 7Li—7Li, 6Li—6Li, and 7Li—6Li with theory permits a thorough investigation of the isotope effect and of the effect of the interaction on the tunnel states. Our findings confirm the tunneling model with <111> off‐center states to be valid even for strongly interacting impurities. Using degenerate perturbation theory in terms of two‐particle states, we obtain essentially exact expressions for the tunneling spectrum and the dynamical susceptibility which agree well with the measured data.
Effective Hamiltonian for scalar theories in the Gaussian approximation
Authors: Naus H. W. L. , Gasenzer T. , Pirner H.‐J. 
Published: May 2007

AbstractWe use a Gaussian wave functional for the ground state to reorder the Hamiltonian into a free part with a variationally determined mass and the rest. Once spontaneous symmetry breaking is taken into account, the residual Hamiltonian can, in principle, be treated perturbatively. In this scheme we analyze the O(1) and O(2) scalar models. For the O(2)‐theory we first explicitly calculate the massless Goldstone excitation and then show that the one‐loop corrections of the effective Hamiltonian do not generate a mass.
Spin depolarization of spreading and propagating wave packets
Authors: Krenzlin H. M. , Kehr K. W. 
Published: May 2007

AbstractSpin relaxation of spin‐1/2 quantum particles on linear chains with random Larmor frequencies is studied. Wave packets are prepared with initial spin polarization in the propagation direction and with either zero, or finite group velocity. The discrete Schrödinger‐Pauli equation is solved numerically. Exponential spin relaxation is observed in a restricted time range. The decay constant depends on the width of the distribution of the Larmor frequencies and on the group velocity. No dependence on the initial halfwidth of the wave packet is found.
Magnetic moment of a two‐dimensional degenerate electron gas in mesoscopic samples
Authors: Ovchinnikov Yu. N. , Lehle W. , Schmid A. 
Published: May 2007

AbstractThe orbital magnetism of two‐dimensional electrons in mesoscopic samples is studied in models where the interaction between electrons is neglected. Various geometries are considered as there are disc, plaquette, bracelet with hard wall confinement and also a confinement with a parabolic potential. We calculate the average magnetic moment which means an average with respect to size fluctuations and de Haas‐van Alphen oscillations which arise in the case of a sharp Fermi cutoff. We see three distinct ranges in the magnetic field: (i) small field region where perturbation theory applies; (ii) moderate fields where edge currents play a prominent role; and (iii) the high field range with a Landau type susceptibility. In a quasiclassical picture, the electronic orbits are not qualitatively changed by a magnetic field in (i); skipping orbits are important in (ii); and in (iii), the cyclotron radius is smaller than the sample size. As a rule, we find an enhancement of the magnetic response which increases with kFL, that is, with sample size divided by the Fermi wave length. Also, we have found out that the quasiclassical approximation fails in the calculation of the magnetic properties; on the other hand, we have seen no essential differences between the canonical ensemble (fixed particle number) and the grand canonical ensemble (chemical potential given). In the case of plaquettes, in particular for samples in the form of squares, we have found agreement with experimental results by Lévy, Reich, Pfeiffer and West.
Non‐linear conductivity of charge‐density‐wave systems
Authors: Werner C. R. , Eckern U. 
Published: May 2007

AbstractWe consider the problem of sliding motion of a charge‐density‐wave subject to static disorder within an elastic medium model. Starting with a field‐theoretical formulation, which allows exact disorder averaging, we propose a self‐consistent approximation scheme to obtain results beyond the standard large‐velocity expansion. Explicit calculations are carried out in three spatial dimensions. For the conductivity, we find a strong‐coupling regime at electrical fields just above the pinning threshold. Phase and velocity correlation functions scale differently from the high‐field regime, and static phase correlations converge to the pinned‐phase behaviour. The sliding charge‐density‐wave is accompanied by narrow‐band noise.
Synthesis, larvicidal, QSAR and structural studies of some triorganotin 2,2,3,3‐tetramethylcyclopropanecarboxylates
Authors: Song Xueqing , Zapata Alejandra , Hoerner Jana , de Dios Angel C. , Casabianca Leah , Eng George 
Published: May 2007

AbstractA series of triorganotin 2,2,3,3‐tetramethylcyclopropanecarboxylates, where R = methyl, ethyl, n‐propyl, n‐butyl, phenyl and cyclohexyl, have been synthesized. Elemental analysis, Mössbauer, infrared and NMR spectroscopies were used to characterize their structures. Based on the spectroscopic results, all the complexes in the solid state with the exception of the tricyclohexyl compound were found to be five‐coordinated, while the tricyclohexyltin derivative was determined to be four‐coordinated. Based on the NMR results, all the complexes in solution have a tetrahedral configuration. Larvicidal activities of the complexes were evaluated against the second instar stage of the Aedes aegypti, Anopheles stephensi and Culex pipiens quinquefasciatus mosquitoes. The toxicity results indicated that this series of triorganotins are effective larvicides against all three species of larvae. In addition, quantitative structure–activity relationships (QSARs) were also developed for each species of larvae. Copyright © 2007 John Wiley & Sons, Ltd.
Organotin compounds containing four‐membered distannoxane [Sn(µ‐OH)]2 units
Authors: Chandrasekhar Vadapalli , Singh Puja , Gopal Kandasamy 
Published: May 2007

AbstractCompounds containing the distannoxane core [Sn(µ‐OH)]2 are reviewed. Synthesis and structural aspects of these compounds are summarized in this article. Copyright © 2007 John Wiley & Sons, Ltd.
First 1,1‐organoboration reactions of vinyltin compounds—a route to boryl‐substituted stannolanes and organo‐substituted stannol‐3‐enes
Authors: Wrackmeyer Bernd , Tok Oleg L. 
Published: May 2007

AbstractDimethyl(divinyl)tin 1 reacts with triethylborane, BEt3 2a, triallylborane, BAll3 2b, tribenzylborane, BBz3 2c, trivinylborane, BVin3 2d, triphenylborane, BPh3 2e, and 1‐boraadamantane 2f by intermolecular 1,1‐organoboration via cleavage of the Snvinyl bond, followed by ring closure via intramolecular 1,1‐organoboration (cleavage of the second Snvinyl bond) to give the boryl‐substituted stannolanes 3a–e, and 7 and 8. The heterocycles 3a–e can undergo dehydroboration, hydroboration, and/or further reactions. If dialkylboranes such as 9‐borabicylo[3.3.1]nonane 11 (9‐BBN) or diethylborane (Et2BH) 12 are used, the first expected step is the hydroboration of one of the vinyl groups in 1, and the second step is the ring closure to boryl‐substituted stannolanes 13 and 6a, respectively, by intramolecular 1,1‐organoboration. The mechanism of the second step, in contrast to the literature, was confirmed by the reaction of dimethyl‐ (9) and diphenyl(di‐2‐propenyl)tin (10) with the boron hydrides 11 and 12. In the resulting stannolanes 14 and 15, the 3,5‐positions of the methyl groups support the mechanism of 1,1‐organoboration. The structures of the new cyclic organotin compounds are assigned on the basis of consistent one‐ and two‐dimensional 1H, 11B, 13C and 119Sn NMR spectroscopic data sets. Copyright © 2007 John Wiley & Sons, Ltd.
Role of GTPases in ribosome assembly
Authors: Karbstein Katrin 
Published: May 2007

AbstractGTPases are a universally conserved class of regulatory proteins involved in such diverse cellular functions as signal transduction, translation, cytoskeleton formation, and intracellular transport. GTPases are also required for ribosome assembly in eukaryotes and bacteria, where they present themselves as possible regulatory molecules. Strikingly, in bacteria they represent the largest class of essential assembly factors. A review of their common structural, biochemical and genetic interactions is presented and integrated with models for their function in ribosome assembly. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 1–11, 2007This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Size of surgical margin does not influence recurrence rates after curative liver resection for colorectal cancer liver metastases
Authors: Bodingbauer M , Tamandl D , Schmid K , Plank C , Schima W , Gruenberger T 
Published: May 2007

Abstract

Background
The aim of this study was to examine the relationship between surgical margin status and site of recurrence after potentially curative liver resection for colorectal metastases using an ultrasonic dissection technique.

Methods
Between January 2000 and December 2003, 176 patients underwent liver resection with curative intent for colorectal metastases at a single institution. Demographics, operative data, pathological margin status, site of recurrence and long-term survival data were collected prospectively and analysed.

Results
On pathological analysis, resection margins were positive in 43 patients, negative by 1–9 mm in 110, and clear by more than 9 mm in 23 patients. At a median follow-up of 33 months, 133 of 176 patients had developed a recurrence, only five of whom had recurrence at the surgical margin. Recurrence at the surgical margin was not significantly related to the size of the margin. Overall, the median time to recurrence was 12·6 months, which was independent of surgical margin size, although there was a significantly higher proportion of patients with multiple metastases in the group with a positive margin (P = 0·008). Margin status did not correlate significantly with either recurrence-free or overall survival.

Conclusion
The rate of recurrence at the surgical margin was low and a positive margin was not associated with an increased risk of recurrence either at the surgical margin or elsewhere.
Excision biopsy of breast lesions changes the pattern of lymphatic drainage
Authors: Estourgie S H , Valdés Olmos R A , Nieweg O E , Hoefnagel C A , Rutgers E J T , Kroon B B R 
Published: May 2007

Abstract

Background
The aim was to validate the sentinel node biopsy procedure in women who had previous breast excision biopsy by means of determining the reproducibility of lymphoscintigraphy after surgery.

Methods
Twenty-five women scheduled for excision biopsy of a breast lesion were investigated. The day before surgery, 99mTc-labelled nanocolloid was injected into the tumour. Lymphoscintigraphy was repeated a minimum of 2 weeks after surgery.

Results
Preoperative lymphoscintigraphy visualized at least one sentinel node in all 25 women. Discrepancy in the drainage patterns after surgery was noted in 17 of 25 patients. A change in the drainage pattern in the axilla after excision biopsy was seen in 11 women. Drainage to the internal mammary chain was noted before surgery in 13 women, but only three had the same drainage pathways after excision biopsy.

Conclusion
After breast excision biopsy lymphoscintigraphy usually showed a different drainage pattern. This implies that sentinel node biopsy should be performed before excision biopsy to ensure optimal sensitivity.
Final 12-year follow-up of Surgery versus Surveillance in the UK Small Aneurysm Trial
Authors:   UK Small Aneurysm Trial participants, Powell J T 
Published: May 2007

Abstract

Background
The aim was to determine whether early open surgical repair would benefit patients with small abdominal aortic aneurysm compared with surveillance on long-term follow-up.

Methods
The 1090 patients who were enrolled into the UK Small Aneurysm Trial between 1991 and 1995 were followed up for aneurysm repair and mortality until November 2005.

Results
By November 2005, 714 patients (65·5 per cent) had died, 929 (85·2 per cent) had undergone aneurysm repair, 150 (13·8 per cent) had died without aneurysm repair and 11 (1·0 per cent) remained alive without aneurysm repair. After 12 years, mortality in the surgery and surveillance groups was 63·9 and 67·3 per cent respectively, unadjusted hazard ratio 0·90 (P = 0·139). Three-quarters of the surveillance group eventually had aneurysm repair, with a 30-day elective mortality of 6·3 per cent (versus 5·0 per cent in the early surgery group, P = 0·366). Estimates suggested that the cost of treatment was 17 per cent higher in the early surgery group, with a mean difference of £1326. The death rate in these patients was about twice that in the population matched for age and sex.

Conclusion
There was no long-term survival benefit of early elective open repair of small abdominal aortic aneurysms. Even after successful aneurysm repair, the mortality among these patients was higher than in the general population.
VBHOM, a data economic model for predicting the outcome after open abdominal aortic aneurysm surgery
Authors: Tang T , Walsh S R , Prytherch D R , Lees T , Varty K , Boyle J R 
Published: May 2007

Abstract

Background
Vascular Biochemistry and Haematology Outcome Models (VBHOM) adopted the approach of using a minimum data set to model outcome. This study aimed to test such a model on a cohort of patients undergoing open elective and non-elective abdominal aortic aneurysm (AAA) repair.

Methods
A binary logistic regression model of risk of in-hospital mortality was built from the 2002–2004 submission to the UK National Vascular Database (NVD) (2718 patients). The subset of NVD data items used comprised serum levels of urea, sodium and potassium, haemoglobin, white cell count, sex, age and mode of admission. The model was applied prospectively using Hosmer–Lemeshow methodology to a test data set from the Cambridge Vascular Unit.

Results
The validation set contained 327 patients, of whom 208 had elective AAA repair and 119 had emergency repair of a ruptured AAA. Outcome following elective and non-elective AAA repair could be described accurately using the same model. The overall mean predicted risk of death was 14·13 per cent, and 48 deaths were predicted. The actual number of deaths was 53 (χ2 = 8·40, 10 d.f., P = 0·590; no evidence of lack of fit). The model also demonstrated good discrimination (c-index = 0·852).

Conclusion
The VBHOM approach has the advantage of using simple, objective clinical data that are easy to collect routinely. The VBHOM data items potentially allow prediction of risk in an individual patient before aneurysm surgery.
Meta-analysis of epidural analgesia versus parenteral opioid analgesia after colorectal surgery
Authors: Marret E , Remy C , Bonnet F 
Published: May 2007

Abstract

Background
Epidural analgesia (EA) with local anaesthetic is considered to play a key role after colorectal surgery. However, its effect on postoperative recovery is still a matter of debate.

Methods
A systematic review of randomized controlled trials comparing postoperative EA and parenteral opioid analgesia after colorectal surgery was performed. The effect on postoperative recovery was evaluated in terms of length of hospital stay, pain intensity, duration of postoperative ileus, incidence of postoperative complications and side-effects.

Results
Sixteen trials published between 1987 and 2005 were included. EA significantly reduced pain scores and duration of ileus (weighted mean difference − 1·55 (95 per cent confidence interval (c.i.) − 2·27 to − 0·84) days). On the other hand, it was associated with a significant increase in the incidence of pruritus (odds ratio (OR) 4·8 (95 per cent c.i. 1·3 to 17·0)), urinary retention (OR 4·3 (1·2 to 15·9)) and arterial hypotension (OR 13·5 (4·0 to 57·7)). EA did not influence duration of hospital stay.

Conclusion
Despite improved analgesia and a decrease in ileus, EA has some adverse effects and does not shorten the duration of hospital stay after colorectal surgery.
Über das 1.2;45‐Dibenz‐suberon‐(3)
Authors: Treibs Wilhelm , Klinkhammer Hans‐Joachim 
Published: May 2007

AbstractDurch cyclisierende Kondensation der Dibenzyl‐0‐carbonsäure wurde das tricyclische 1.2;4.5‐Dibenz‐suberon‐(3) dargestellt. Einige Abwandlungen des Ketons sowie einige Reaktionen des bicyclischen 1.2‐Benz‐suberons‐(3) werden beschrieben.
Zur Kenntnis des Dichlor‐formoxims
Authors: Seher Artur 
Published: May 2007

AbstractErsatz des Sauerstoffs im Phosgen durch die Oxim‐Gruppe verändert die Reaktionsweise der Verbindung grundsätzlich. Die Zersetzung des Dichlor‐formoxims konnte als Gleichgewichtsreaktion geklärt werden. Weiter wurden Molekülverbindungen aus Dichlor‐formoxim und Diäthern aufgefunden.