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AimsDespite general awareness that screening for atrial fibrillation (AF) could reduce health hazards, large-scale implementation is lagging behind technological developments. As the successful implementation of a screening programme remains challenging, this study aims to identify facilitating and inhibiting factors from healthcare providers’ perspectives.Methods and resultsA mixed-methods approach was used to gather data among practice nurses in primary care in the southern region of the Netherlands to evaluate the implementation of an ongoing single-lead electrocardiogram (ECG)-based AF screening programme. Potential facilitating and inhibiting factors were evaluated using online questionnaires (N = 74/75%) and 14 (of 24) semi-structured in-depth interviews (58.3%). All analyses were performed using SPSS 26.0. In total, 16 682 screenings were performed on an eligible population of 64 000, and 100 new AF cases were detected. Facilitating factors included ‘receiving clear instructions’ (mean ± SD; 4.12 ± 1.05), ‘easy use of the ECG-based device’ (4.58 ± 0.68), and ‘patient satisfaction’ (4.22 ± 0.65). Inhibiting factors were ‘time availability’ (3.20 ± 1.10), ‘insufficient feedback to the practice nurse’ (2.15 ± 0.89), ‘absence of coordination’ (54%), and the ‘lack of fitting policy’ (32%).ConclusionLarge-scale regional implementation of an AF screening programme in primary care resulted in a low participation of all eligible patients. Based on the perceived barriers by healthcare providers, future AF screening programmes should create preconditions to fit the intervention into daily routines, appointing an overall project lead and a General Practitioner (GP) as a coordinator within every GP practice.

One of the manifestations of chirality-induced spin selectivity is the appearance of a magnetocurrent. Magnetocurrent is defined as the difference between the charge currents at finite bias in a two terminal device for opposite magnetizations of one of the leads. In experiments on chiral molecules assembled in monolayers the magnetocurrent is dominantly odd in bias voltage, while theory often yields an even one. From theory it is known that the spin–orbit coupling and chirality of the molecule can only generate a finite magnetocurrent in the presence of interactions, either of the electrons with vibrational modes or among themselves, through the Coulomb interaction. Here we analytically show that the magnetocurrent in bipartite-chiral structures mediated through Coulomb interactions is exactly even in the wide band limit and exactly odd for semi-infinite leads due to the bipartite lattice symmetry of the Green’s function. Our numerical results confirm these analytical findings.

This is the code used for the publication "CISS Effect: A Magnetoresistance Through Inelastic Scattering"., This publication is part of the project "CISS" (with project number 680.92.18.01) of the research programme "Natuur- kunde Vrije Programma's" which is financed by the Dutch Research Council (NWO)

Although molecular rectifiers were proposed over four decades ago 1,2 , until recently reported rectification ratios (RR) were rather moderate 2–11 (RR ~ 101). This ceiling was convincingly broken using a eutectic GaIn top contact 12 to probe molecular monolayers of coupled ferrocene groups (RR ~ 105), as well as using scanning tunnelling microscopy-break junctions 13–16 and mechanically controlled break junctions 17 to probe single molecules (RR ~ 102–103). Here, we demonstrate a device based on a molecular monolayer in which the RR can be switched by more than three orders of magnitude (between RR ~ 100 and RR ≥ 103) in response to humidity. As the relative humidity is toggled between 5% and 60%, the current–voltage (I–V) characteristics of a monolayer of di-nuclear Ru-complex molecules reversibly change from symmetric to strongly asymmetric (diode-like). Key to this behaviour is the presence of two localized molecular orbitals in series, which are nearly degenerate in dry circumstances but become misaligned under high humidity conditions, due to the displacement of counter ions (PF6 –). This asymmetric gating of the two relevant localized molecular orbital levels results in humidity-controlled diode-like behaviour. The rectification ratio of a molecular junction made of a self-assembled monolayer of di-nuclear ruthenium-complex molecules can be varied by more than three orders of magnitude by controlling relative humidity.

Rectification has been at the foundation of molecular electronics. Most single-molecule diodes realized experimentally so far are based on asymmetries in the coupling with the electrodes or using the donor–acceptor principle. In general, however, their rectification ratios are usually small (

This paper examines charge transport by tunneling across a series of electrically insulating molecules with the structure HS(CH2)4CONH(CH2)2R) in the form of self-assembled monolayers (SAMs), supported on silver. The molecules examined were studied experimentally by Yoon et al. (Angew. Chem. Int. Ed. 2012, 51, 4658-4661), using junctions of the structure AgS(CH2)4CONH(CH2)2R//Ga2O3/EGaIn. The tail group R had approximately the same length for all molecules, but a range of different structures. Changing the R entity over the range of different structures (aliphatic to aromatic) does not influence the conductance significantly. To rationalize this surprising result, we investigate transport through these SAMs theoretically, using both full quantum methods and a generic, independent-electron tight-binding toy model. We find that the highest occupied molecular orbital, which is largely responsible for the transport in these molecules, is always strongly localized on the thiol group. The relative insensitivity of the current density to the structure of the R group is due to a combination of the couplings between the carbon chains and the transmission inside the tail. Changing from saturated to conjugated tail groups increases the latter but decreases the former. This work indicates that significant control over SAMs largely composed of nominally insulating groups may be possible when tail groups are used that are significantly larger than those used in the experiments of Yoon et al.1.

Molecular electronics aims at exploiting the internal structure and electronic orbitals of molecules to construct functional building blocks(1). To date, however, the overwhelming majority of experimentally realized single-molecule junctions can be described as single quantum dots, where transport is mainly determined by the alignment of the molecular orbital levels with respect to the Fermi energies of the electrodes(2) and the electronic coupling with those electrodes(3,4). Particularly appealing exceptions include molecules in which two moieties are twisted with respect to each others(5,6) and molecules in which quantum interference effects are possible(7,8). Here, we report the experimental observation of pronounced negative differential conductance in the current-voltage characteristics of a single molecule in break junctions. The molecule of interest consists of two conjugated arms, connected by a non-conjugated segment, resulting in two coupled sites. A voltage applied across the molecule pulls the energy of the sites apart, suppressing resonant transport through the molecule and causing the current to decrease. A generic theoretical model based on a two-site molecular orbital structure captures the experimental findings well, as confirmed by density functional theory with non-equilibrium Green's functions calculations that include the effect of the bias. Our results point towards a conductance mechanism mediated by the intrinsic molecular orbitals alignment of the molecule.

We investigate transport through mechanically triggered single-molecule switches that are based on the coordination sphere-dependent spin state of Fe(II)-species. In these molecules, in certain junction configurations the relative arrangement of two terpyridine ligands within homoleptic Fe(II)-complexes can be mechanically controlled. Mechanical pulling may thus distort the Fe(II) coordination sphere and eventually modify their spin state. Using the movable nanoelectrodes in a mechanically controlled break-junction at low temperature, current-voltage measurements at cryogenic temperatures support the hypothesized switching mechanism based on the spin-crossover behavior. A large fraction of molecular junctions formed with the spin-crossover-active Fe(II)-complex displays a conductance increase for increasing electrode separation and this increase can reach 1-2 orders of magnitude. Theoretical calculations predict a stretching-induced spin transition in the Fe(II)-complex and a larger transmission for the high-spin configuration.

In the pursuit of down-sizing electronic components, the ultimate limit is the use of single molecules as functional devices. The first theoretical proposal of such a device, predicted more than four decades ago, is the seminal Aviram–Ratner rectifier that exploits the orbital structure of the molecule. The experimental realization of single-molecule rectifiers, however, has proven to be challenging. In this work, we report on the experimental realization of a gate-tunable single-molecule rectifier with rectification ratios as high as 600. The rectification mechanism arises from the molecular structure and relies on the presence of two conjugated sites that are weakly coupled through a saturated linker. The observed gate dependence not only demonstrates tunability of the rectification ratio, it also shows that the proposed rectification mechanism based on the orbital structure is operative in the molecule.

Vibrational excitations have an important effect on the transportproperties of molecular junctions. Which modes are importantdepends strongly on the coupling of the molecule to the leads. Inthis chapter we analyze these effects for both strongly and weaklycoupled molecules and give approximate selection rules for thevibrational modes. For weakly coupledmolecules the low-frequencymodes tend to be dominant. Their relative intensities are deter-mined by the so-called Franck-Condon factors. For strongly coupledconjugated molecules, on the other hand, the modes involvingstretching of the π -bonds determine the transport properties. Thischapter shows how to calculate vibrational effects in both regimesfor the full vibrational spectrum of a molecule.

We present a novel implementation of the first-principles approach to molecular charge transport using the non-equilibrium Green's function formalism in combination with the ADF/BAND periodic band-structure DFT code, together with results for several example systems. As a proof of concept, we first discuss transport calculations on 1D chains of Li and Al atoms. We then present a detailed study of BDT and archetypal molecular wires from the OPE-family, sandwiched between 3D Au contacts, comparing well with results from the literature. Our implementation further allows us to make a comparison of 3D contacts with and without periodic boundary conditions, the latter being particularly useful for modeling the needle-shaped contacts used in break-junction experiments.

We examine the Raman spectra of a series of molecules in different charge states and suggest ways of controlling these charge states in charge transport experiments. Our study uses density functional theory (DFT)-based quantum chemical methods. The molecules we study are benzene derivatives, which accommodate transport either through the HOMO or the LUMO (where the HOMO and the LUMO denote the highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively). We have investigated whether observable differences in the Raman spectra will occur upon electron addition or removal. We find substantial frequency shifts upon electron removal or addition. These shifts tend to be uniformly downward in the case of LUMO transport, whereas, for HOMO transport, this unidirectionality is lacking and it is due to the fact that anions are usually less strongly bound than neutrals, whereas removing an electron from a bonding-type orbital usually gives localized modification in bond length and strength.

One of the hallmark symptoms of patients with chronic heart failure (CHF) is exercise intolerance. Therefore, exercise testing has become an important tool for the evaluation and monitoring of heart failure. Whereas the maximal aerobic capacity (peak VO(2)) is a reliable indicator of the severity and prognosis of heart failure, submaximal exercise parameters may be more closely related to the ability to perform daily activities. As such, oxygen (O(2)) uptake kinetics, describing the rate change of O(2) uptake during onset or recovery of submaximal constant-load exercise (O(2) onset and recovery kinetics, respectively), have been shown to be useful parameters for objectively evaluating the functional capacity of CHF patients. However, their evaluation in this population is not a routine part of daily clinical practice. Possible reasons for this include a lack of standardisation of the assessment methodology and a limited number of studies evaluating the clinical use of O(2) uptake kinetics in CHF patients. In addition, the pathophysiological mechanisms underlying the delay in O(2) uptake kinetics in these patients are not completely understood. This review discusses the current literature on the clinical potency and physiological determinants of O(2) uptake kinetics in CHF patients and provides directions for future research. (Neth Heart J 2009;17:238-44.Neth Heart J 2009;17:238-44.).

The derivation of the contralateral effect from EOG data is presented. The mathematical procedure can be adapted to special experimental conditions, such as unilateral occlusion, and asymmetric fixation, or for instance to a group of patients with unilateral enucleation. The contralateral spread of the standing potential of the eye is significantly shown by the experimental results, and is expressed by a factor f. This factor is of the order of 15% and represents the fraction of the ipsilateral potential that is measured contralaterally. A method is given to correct the EOG data in case of unilateral impairment.

The EOG is influenced by the corneo-retinal potential of the contralateral eye. This contralateral influence results in polarity reversal in severely destructed eyes which do not have their own corneo-retinal potential. In eyes with a decreased corneo-retinal potential the contralateral effect can cause polarity reversal only during the light adapted period. Contralateral influence on eyes with abolished light sensitive component but a relatively well preserved light-insensitive component results in a paradoxical curve. Deterioration of the light-sensitive part of the EOG concerns primarily the positive component. In severely impaired eyes the EOG value should be corrected to allow for the influence of the contralateral sound eye; a formula, devised for calculating the corrected values, is given in a second paper.

In this review, we consider single-electron effects in transport through nanoscale devices. These effects are ubiquitous in quantum dot physics, but in recent years their occurrence in molecular transport has triggered important new research efforts. In this case, the experimental results show a rich variety of features which make it possible to extract a wealth of information about the physics of these structures. We shall show that most of this information can be extracted in the case where the coupling of the active region to the leads is weak. However, between the strong and weak coupling regimes, that is, at intermediate coupling, we can observe the richest behaviour. We shall very briefly outline the physics of different transport processes through three-terminal devices and then focus on the single-electron effects. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a method for incorporating image-charge effects into the description of charge transport through molecular devices. A simple model allows us to calculate the adjustment of the transport levels, due to the polarization of the electrodes as charge is added to and removed from the molecule. For this, we use the charge distributions of the molecule between two metal electrodes in several charge states, rather than in gas phase, as obtained from a density-functional theory-based transport code. This enables us to efficiently model level shifts and gap renormalization caused by image-charge effects, which are essential for understanding molecular transport experiments. We apply the method to benzene di-amine molecules and compare our results with the standard approach based on gas phase charges. Finally, we give a detailed account of the application of our approach to porphyrin-derivative devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8, 282 (2013)], which demonstrates the importance of accounting for image-charge effects when modeling transport through molecular junctions.

Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelec- tric response of a series of molecules featuring a quinoid core using density functional theory (DFT), as well as a semi-empirical interacting model Hamiltonian describing the {\pi}-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdraw- ing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S^2G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices., Comment: 22 pages, 11 figures

Item does not contain fulltext We propose a design for realizing quantum charge pump based on a recent proposal for a molecular motor (Seldenthuis J S et al 2010 ACS Nano 4 6681). Our design is based on the presence of a moiety with a permanent dipole moment which can rotate, thereby modulating the couplings to metallic contacts at both ends of the molecule. Using the non-equilibrium Keldysh Green's function formalism (NEGF), we show that our design indeed generates a pump current. In the non-interacting pump, the variation of frequency from adiabatic to non-adiabatic regime, can be used to control the direction as well as the amplitude of the average current. The effect of Coulomb interaction is considered within the first- and the second- order perturbation. The numerical implementation of the scheme is quite demanding, and we develop an analytical approximation to obtain a speed-up giving results within a reasonable time. We find that the amplitude of the average pumped current can be controlled by both the driving frequency and the Coulomb interaction. The direction of of pumped current is shown to be determined by the phase difference between left and right anchoring groups.

Natural evolution is widely accepted as being the process underlying the design and optimization of the sensory functions of biological organisms. Using a genetic algorithm, this process is extended to the automatic optimization and design of optical systems, e.g. as used in astronomical telescopes. The results of this feasibility study indicate that various types of aberrations can be corrected quickly and simultaneously, even on small computers.

A new method is given for calculating the electronic structure of solids, enabling finite-difference methods to be used for systems with deep atomic potentials. In muffin-tin spheres around the nuclei, the atomic wave functions are determined using standard numerical techniques. They are then matched onto a finite-difference grid in the interstitial region by an embedding procedure by which the interior of a muffin-tin is replaced by an embedding potential at its boundary. The sparse Hamiltonian matrix of the grid can be diagonalized using methods with time scaling linear with the system size. We present results for f.c.c. copper.

In molecular charge transport, transition voltage spectroscopy (TVS) holds the promise that molecular energy levels can be explored at bias voltages lower than required for resonant tunneling. We investigate the theoretical basis of this tool using a generic model. In particular, we study the length dependence of the conducting frontier orbital and of the “transition voltage” as a function of length. We show that this dependence is influenced by the amount of screening of the electrons in the molecule, which determines the voltage drop at the contacts or across the entire molecule. We observe that the transition voltage depends significantly on the length, but the ratio between the transition voltage and the conducting frontier orbital is approximately constant only in strongly screening (conjugated) molecules. Uncertainty about the screening within a molecule thus limits the predictive power of TVS. We furthermore argue that the relative length independence of the transition voltage for nonconjugated chains is due to strong localization of the frontier orbitals on the end groups ensuring binding of the rods to the metallic contacts. Finally, we investigate the characteristics of TVS in asymmetric molecular junctions. If a single level dominates the transport properties, TVS can provide a good estimate for both the level position and the degree of junction asymmetry. If more levels are involved, the applicability of TVS becomes limited.

We present a method which uses density functional theory (DFT) to treat transport through a single molecule connected to two conducting leads for the weak and intermediate coupling. This case is not accessible to standard nonequilibrium Green’s function calculations. Our method is based on a mapping of the Hamiltonian on the molecule to a limited set of many-body eigenstates. This generates a many-body Hamiltonian with parameters obtained from ground-state local (spin) density approximation-DFT calculations. We then calculate the transport using many-body Green’s function theory. We compare our results with existing density matrix renormalization group calculations for spinless and for spin-1/2 fermion chains and find good agreement.

We investigated contractile responses of the isolated human coronary artery to 5-hydroxytryptamine (5-HT), washed human platelets, sumatriptan and ergotamine. 5-HT (pD2: 6.8 +/- 0.1, Emax: 47.7 +/- 6.8 mN) and platelets (effect 14.4 +/- 2.8 mN with 3.10(10) platelets/l) caused contractile responses which were attenuated by ketanserin (1 microM). In the presence of ketanserin (1 microM), both rauwolscine (1 and 10 microM) and cyanopindolol (1 and 10 microM) caused concentration-dependent additional antagonism against contractions induced by low (< or = 1 microM) concentrations of 5-HT. Sumatriptan-induced contractions (pD2: 6.2 +/- 0.1; Emax: 10.7 +/- 2.4 mN) were antagonized to a similar extent by both rauwolscine (1 microM) and cyanopindolol (1 microM) (pKB: 6.5 +/- 0.1 and 6.4 +/- 0.1, respectively) and also by metergoline (0.1 microM; pKB: 7.2 +/- 0.1). The order of potency of antagonists against sumatriptan resembles the order reported for the human saphenous vein 5-HT1D-like receptor. No significant additional antagonism by cyanopindolol (1 microM) or rauwolscine (1 microM) against platelet-induced contractile responses was observed. Ergotamine caused potent contractile responses (pD2: 8.4 +/- 0.3, Emax: 19.4 +/- 2.4 mN). It is concluded that although 5-HT2 receptors predominantly mediate 5-HT-induced contractions, the 5-HT1-like receptor seems to play a role in coronary vasospasm caused by low concentrations of 5-HT.

Most studies concerning 3D strain imaging of the heart report on 3D speckle tracking techniques, using the envelope data for tissue tracking. In this study, an RF-based 3D strain imaging technique was applied to 3D (t) RF-data of the left ventricle. RF-data are not commercially available but have proven to yield a higher strain accuracy in all directions. The data were acquired in 6 young healthy children (6-14 yrs). A 3D free-shape coarse-to-fine displacement tracking algorithm was applied to the 3D RF-data, yielding the frame-to-frame 3D displacement fields. A 3D ellipsoidal function was fit through several manually segmented slices of the 3D volume. This 3D ellipsoid was tracked over the entire cardiac cycle, yielding the cumulative radial, circumferential and longitudinal strains. Results show 3D strain (radial, circumferential and longitudinal) within the entire left ventricle for different phases of the cardiac cycle. The shapes of the averaged strain curves are in well accordance with published curves. The image quality in the inferior and anterior wall seems to be less optimal for accurate strain imaging, leading to reduced strain values in these regions. In conclusion, 3D (t) strain imaging is on the rise, and RF-based tracking will play an important role in the near future.

We have applied a fluids density functional theory based on that of Yu and Wu [J. Chem. Phys. 116, 7094 (2002)] to treat reversible supramolecular polymers near a hard surface. This approach combines a hard-sphere fluids density functional theory with the first-order thermodynamic perturbation theory of Wertheim. The supramolecular polymers are represented in the theory by hard-spheres with two associating sites. We explore the effects of the bonding scheme, monomer concentration, and association energy upon the equilibrium chain sizes and the depletion lengths. This study is performed on simple systems containing two-site monomers and binary mixtures of two-site monomers combined with end stopper monomers which have only a single association site. Our model has correct behavior in the dilute and overlap regimes and the bulk results can be easily connected to simpler random-flight models. We find that there is a nonmonotonic behavior of the depletion length of the polymers as a function of concentration and that this depletion length can be controlled through the concentration of end stoppers. These results are applicable to the study of colloidal dispersions in supramolecular polymer solutions.

In this chapter, single-electron effects in transport through nanoscale devices are considered. Although these effects are ubiquitous in quantum dot physics, during recent years their observation in molecular transport has triggered important new research efforts. In this case, the experimental results have shown a rich variety of features which enables much information to be extracted regarding the physics of these structures. Most of this information can be obtained in the case where coupling of the active region to the leads is weak, which is in direct contrast to the limits described in Chapter 1 of this volume. It should be noted, however, the richest behavior can be observed precisely on the border of the two regimes – that is, with intermediate coupling. In addition, a very brief outline will be provided of the physics of different transport processes through three-terminal devices, with subsequent information focused on single-electron effects. Keywords: quantum transport; Coulomb blockade; single-electron effects; quantum dots; single-molecule electronics; three-terminal devices

We have combined ab initio quantum chemistry calculations with a rate-equation formalism to analyze electroluminescence spectra in single-molecule junctions, measured recently by several groups in Scanning Tunneling Microscope setups. In our method, the entire vibrational spectrum is taken into account. Our method leads to good quantitative agreement with both the spectroscopic features of the measurements and their current and voltage dependence. Moreover, our method is able to explain several previously unexplained features. We show that in general, the quantum yield is expected to be suppressed at high bias, as is observed in one of the measurements. Additionally, we comment on the influence of the vibrational relaxation times on several features of the spectrum., Comment: 9 pages, 12 figures

CHF (chronic heart failure) is associated with a prolonged recovery of skeletal muscle energy stores following submaximal exercise, limiting the ability to perform repetitive daily activities. However, the pathophysiological background of this impairment is not well established. The aim of the present study was to investigate whether muscle metabolic recovery following submaximal exercise in patients with CHF is limited by O2 delivery or O2 utilization. A total of 13 stable CHF patients (New York Heart Association classes II-III) and eight healthy subjects, matched for age and BMI (body mass index), were included. All subjects performed repetitive submaximal dynamic single leg extensions in the supine position. Post-exercise PCr (phosphocreatine) resynthesis was assessed by 31P-MRS (magnetic resonance spectroscopy). NIRS (near-IR spectroscopy) was applied simultaneously, using the rate of decrease in HHb (deoxygenated haemoglobin) as an index of post-exercise muscle re-oxygenation. As expected, PCr recovery was slower in CHF patients than in control subjects (time constant, 47 ± 10 compared with 35 ± 12 s respectively; P=0.04). HHb recovery kinetics were also prolonged in CHF patients (mean response time, 74±41 compared with 44±17 s respectively; P=0.04). In the patient group, HHb recovery kinetics were slower than PCr recovery kinetics (P=0.02), whereas no difference existed in the control group (P=0.32). In conclusion, prolonged metabolic recovery in CHF patients is associated with an even slower muscle tissue re-oxygenation, indicating a lower O2 delivery relative to metabolic demands. Therefore we postulate that the impaired ability to perform repetitive daily activities in these patients depends more on a reduced muscle blood flow than on limitations in O2 utilization. © The Authors Journal compilation © 2010 Biochemical Society.

Many types of molecular motors have been proposed and synthesized in recent years, displaying different kinds of motion, and fueled by different driving forces such as light, heat, or chemical reactions. We propose a new type of molecular motor based on electric field actuation and electric current detection of the rotational motion of a molecular dipole embedded in a three-terminal single-molecule device. The key aspect of this all-electronic design is the conjugated backbone of the molecule, which simultaneously provides the potential landscape of the rotor orientation and a real-time measure of that orientation through the modulation of the conductivity. Using quantum chemistry calculations, we show that this approach provides full control over the speed and continuity of motion, thereby combining electrical and mechanical control at the molecular level over a wide range of temperatures. Moreover, chemistry can be used to change all key parameters of the device, enabling a variety of new experiments on molecular motors., Comment: 15 pages, 7 figures

Traditionally, the effects of physical training in patients with chronic heart failure (CHF) are evaluated by changes in peak oxygen uptake (peak \( \dot{V}{\text{O}}_{2} \)). The assessment of peak \( \dot{V}{\text{O}}_{2} \), however, is highly dependent on the patients’ motivation. The aim of the present study was to evaluate the clinical utility of effort-independent exercise variables for detecting training effects in CHF patients. In a prospective controlled trial, patients with stable CHF were allocated to an intervention group (N = 30), performing a 12-week combined cycle interval and muscle resistance training program, or a control group (N = 18) that was matched for age, gender, body composition and left ventricular ejection fraction. The following effort-independent exercise variables were evaluated: the ventilatory anaerobic threshold (VAT), oxygen uptake efficiency slope (OUES), the \( \dot{V}_{\text{E}} /\dot{V}{\text{CO}}_{ 2} \) slope and the time constant of \( \dot{V}{\text{O}}_{2} \) kinetics during recovery from submaximal constant-load exercise (τ-rec). In addition to post-training increases in peak \( \dot{V}{\text{O}}_{2} \) and peak \( \dot{V}_{\text{E}} , \), the intervention group showed significant within and between-group improvements in VAT, OUES and τ-rec. There were no significant differences between relative improvements of the effort-independent exercise variables in the intervention group. In contrast with VAT, which could not be determined in 9% of the patients, OUES and τ-rec were determined successfully in all patients. Therefore, we conclude that OUES and τ-rec are useful in clinical practice for the assessment of training effects in CHF patients, especially in cases of poor subject effort during symptom-limited exercise testing or when patients are unable to reach a maximal exercise level.

The purpose of this study was to investigate which patient characteristics may predict training effects on maximal and submaximal exercise performance in patients with heart failure. Together with commonly used clinical and performance-related variables, oxygen uptake kinetics during exercise recovery were included as possible predictors. Fifty patients with heart failure (New York Heart Association class II or III) performed a 12-week training program (cycle interval and resistance training). Training effects were expressed as changes in peak oxygen uptake (Vo2), Vo2 at ventilatory threshold (VT), and the time constant of Vo2 recovery after submaximal exercise (τ-rec). After training, peak Vo2, Vo2 at VT, and τ-rec improved significantly, with a wide variety in training responses. Changes in peak Vo2 were related to changes in VT (r = 0.79, p 2 could be predicted by recovery halftime of peak Vo2 (T1/2), peak Vo2 (percentage of predicted), and peak respiratory exchange ratio (R2 = 36%). Post-training changes in VT could be predicted by T1/2 and VT (predicted) (R2 = 29%), whereas changes in τ-rec could be predicted only by τ-rec at baseline (R2 = 34%). In conclusion, oxygen recovery kinetics after maximal and submaximal exercise substantially add to the prediction of training effects in patients with heart failure, presumably because of their relations with, respectively, central and peripheral impairments of exercise capacity. However, the explained variance in training effects is not sufficient to make a definite distinction between training responders and nonresponders.

In bulk systems, molecules are routinely identified by their vibrational spectrum using Raman or infrared spectroscopy. In recent years, vibrational excitation lines have been observed in low-temperature conductance measurements on single molecule junctions and they can provide a similar means of identification. We present a method to efficiently calculate these excitation lines in weakly coupled, gateable single-molecule junctions, using a combination of ab initio density functional theory and rate equations. Our method takes transitions from excited to excited vibrational state into account by evaluating the Franck-Condon factors for an arbitrary number of vibrational quanta, and is therefore able to predict qualitatively different behaviour from calculations limited to transitions from ground state to excited vibrational state. We find that the vibrational spectrum is sensitive to the molecular contact geometry and the charge state, and that it is generally necessary to take more than one vibrational quantum into account. Quantitative comparison to previously reported measurements on pi-conjugated molecules reveals that our method is able to characterize the vibrational excitations and can be used to identify single molecules in a junction. The method is computationally feasible on commodity hardware., Comment: 9 pages, 7 figures

The purpose of this study was to evaluate the accuracy of two techniques for the continuous assessment of cardiac output in patients with chronic heart failure (CHF): a radial artery pulse contour analysis method that uses an indicator dilution method for calibration (LiDCO) and an impedance cardiography technique (Physioflow), using the Fick method as a reference. Ten male CHF patients (New York Heart Association class II–III) were included. At rest, cardiac output values obtained by LiDCO and Physioflow were compared with those of the direct Fick method. During exercise, the continuous Fick method was used as a reference. Exercise, performed on a cycle ergometer in upright position, consisted of two constant-load tests at 30% and 80% of the ventilatory threshold and a symptom-limited maximal test. Both at rest and during exercise LiDCO showed good agreement with reference values [bias ± limits of agreement (LOA), −1% ± 28% and 2% ± 28%, respectively]. In contrast, Physioflow overestimated reference values both at rest and during exercise (bias ± LOA, 48% ± 60% and 48% ± 52%, respectively). Exercise-related within-patient changes of cardiac output, expressed as a percent change, showed for both techniques clinically acceptable agreement with reference values (bias ± LOA: 2% ± 26% for LiDCO, and −2% ± 36% for Physioflow, respectively). In conclusion, although the limits of agreement with the Fick method are pretty broad, LiDCO provides accurate measurements of cardiac output during rest and exercise in CHF patients. Although Physioflow overestimates cardiac output, this method may still be useful to estimate relative changes during exercise.

Continuous assessment of mixed venous oxygen saturation (cSvO(2)) during exercise using a fiber optic pulmonary artery catheter can provide valuable information on the physiological determinants of the exercise capacity in patients with chronic heart failure (CHF). Since its accuracy is not well established during exercise, this study evaluated the reliability of a fiber optic pulmonary artery catheter for measuring SvO(2 )during exercise in CHF patients. Ten patients with stable CHF performed steady-state exercise tests at 30 and 80% of the ventilatory threshold and consequently a symptom-limited incremental exercise test. During the tests, SvO(2 )was monitored continuously using a fiber optic pulmonary artery catheter (CCOmbo, Edwards Lifesciences, Irvine, CA, USA) and by oximetric analysis of mixed venous blood samples obtained at rest (n = 26), steady state (n = 17) and peak exercise (n = 8). There was a significant correlation between oximetrically determined SvO(2) and cSvO(2) values (r = 0.97). The bias between both methods was 0.6% with limits of agreement from -8 to 9%. The limits of agreement for SvO(2 )values30% (n = 16) were slightly wider than for SvO(2) values30% (n = 35) (from -10 to 12% and from -7 to 8%, respectively). In conclusion, continuous measurement of SvO(2 )during exercise using a fiber optic pulmonary catheter is reliable in patients with CHF, with somewhat less accurate measurements of SvO(2 )below 30%.

We discuss the critical behavior of several models, all related to the 19-vertex model. These models combine Ising and Gaussian degrees of freedom and have central charge c=3/2 at the critical point. We present arguments why the frustrated XY model, which also has Gaussian and Ising degrees of freedom, might fall into a different universality class. We use the Monte Carlo transfer-matrix method of Bl\"ote and Nightingale to obtain accurate numerical results for the central charge and exponents of the frustrated XY model. In particular, we test the prediction for the central charge c to be equal to 3/2 also in this model. We find c=1.66\ifmmode\pm\else\textpm\fi{}0.04 for the central charge of the frustrated XY model at the critical point. It is not clear at this stage to which universality class this critical behavior belongs.

Models of biological tissues are described in terms of acoustic parameters and of structure. Beam formation is discussed for continuous wave and pulsed modes of transducer operation and the concept of the point spread function (PSF) is introduced. The PSF is equivalent to the resolution cell, or the sampling volume, of echographic equipment. The generation of echograms from parenchymal tissues is described in terms of speckle formation due to interference at reception on the transducer. The speckle dimensions are quantitatively compared to the sampling volume of the employed transducer. It is shown that for fully developed speckle the tissue characteristics are exclusively reflected in the mean echolevel and not in the speckle size. The speckle size is, however, greatly dependent on the bandwidth, the frequency, and the geometry of the employed transducer. The attenuation by the insonated tissue yields a depth-dependent increase of mainly the lateral speckle size, in addition to the depth dependence caused by the beam formation. If the number density of scattering sites within the tissue is relatively low, the speckle characteristics are dependent on this density and, hence, tissue characterization is feasible if these characteristics are analyzed by statistical methods. These methods are gray level histogram analysis and the estimation of the autocorrelation function, ie, first and second order statistics, respectively. Structural order in tissues can be quantified by autocorrelation analysis and clinical studies on diffuse liver diseases support this conclusion. The effects of pre- and postprocessing on the detectability of focal lesions are outlined. The impact of multifocus systems and of the acquisition of radio frequency echograms on further developments of clinical echography is discussed.

We measured the quantitative ultrasound (QUS) parameters broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus using an ultrasound imaging device (UBIS 3000) in 698 healthy Caucasian male and female subjects (110 prepubertal, 356 pubertal/adolescent and 210 adult) between 6 and 77 years of age. The influence of different region of interest (ROI) diameters (6-20 mm) and software techniques (automatic (ROIaut), copied (ROIcop) and fixed coordinate (ROIfix) measurements) on annual rate of change, trend assessment interval (TAI; an estimate of the follow-up time required for measuring a true change), percentage of positioning errors (positioning of the ROI partly at the cortical edge or even partly beyond the calcaneus) and short-term precision error was studied. When using ROI diameters increasing from 8 to 20 mm, the annual rate of change of BUA and SOS did not change in adults, but was higher in prepubertal subjects (when subjects with positioning errors were excluded) as well as in pubertal/adolescent subjects. TAIs for BUA were shortest when using ROIaut with ROI diameters between 8 and 14 mm (TAI between 1.2 and 1.5 years for prepubertal boys and pubertal/adolescent subjects, 2.4 years for prepubertal girls, 2.7 years for postmenopausal women, and 9 years in men and premenopausal women). TAIs for SOS were 4 years or more, except for postmenopausal women (2.1 years) and prepubertal boys (3.2 years). Measurements with large ROI diameters, especially with fixed region coordinates, resulted in a high percentage of positioning errors and mostly in longer TAIs. Analysis of the short-term precision errors did not reveal these important differences between the various ROI diameters. Our results indicate that calcaneal ultrasound imaging may be useful for measuring skeletal changes in healthy children, especially with BUA, and in postmenopausal women with BUA and SOS using an automatic measurement in the region of lowest attenuation. ROI diameters of 12 mm should be used in prepubertal subjects and of 14 mm in pubertal/adolescent and adult subjects.

A new method for handling multi-physical diffusion problems is presented. This type of problem is relevant in the simulation of semiconductor fabrication, where the diffusion of dopants and point defects determines the electrical properties of the resulting devices. This paper describes some important steps towards the goal of applying a multilevel adaptive grid generation technique to the solution of this problem Immersed interfaces are used, in which the (moving) interface runs in between the grid points — they do not have to lie on the interface. In this paper, we formulate a modified version of the immersed interface method by LeVeque and Li, and show that this new version works well within a multigrid approach on structured grids. Good convergence rates are obtained.

A common problem in teaching students in science or engineering is the decreasing level of formal and practical knowledge of mathematics in recent generations of students. This problem seems to be quite international (although its severity may vary from country to country), and many physics degree courses are in the process of dealing with this problem. Usually the solution (or alleviation) of the problem consists of starting the maths teaching from a more elementary level, with more or less extended reviews of differentiation, integration and complex numbers, and of adopting a less rigorous, less mathematical approach in teaching the more advanced topics. The choice of a suitable textbook is, of course, crucial for the teaching strategy. This new book aims at covering the full range of mathematical topics necessary for physics and engineering degree courses. Therefore it starts with preliminary calculus, differentiation and integration, and proceeds to quite advanced material such as groups and representations, and tensor analysis. It also contains a chapter on numerical analysis. I have compared this book with two other well known texts, Mathematical Methods in the Physical Sciences by Mary L Boas (John Wiley, second edition, 1983, $42.95) and Mathematical Methods for Physicists by George B Arfken and Hans J Weber (Academic Press, fourth edition, 1995 $69.00) (these prices being found on the Internet pages of the respective publishers). All these books treat matrices and vectors, differential equations, special functions, complex analysis, variational calculus, probability theory, Fourier series analysis, vector calculus and integral equations. All three books present the mathematics for physicists and/or engineers rather than for mathematicians, who will, for example, look in vain for epsilon-delta proofs of continuity. The differences between the books are mainly in the level from which they start, in the choice of advanced topics and in the style of presentation. Boas starts off at a rather elementary level, though without reviewing ordinary differentiation and integration. There is nothing on group theory in this book, but it includes tensor analysis. Arfken and Weber's book starts off at a more advanced level: the first chapter deals with vector analysis, including the Gauss and Stokes theorems and the Dirac delta-function, and the second chapter deals already with curved coordinates and tensor analysis. This book contains a chapter on group theory and, interestingly, one on nonlinear methods and chaos. The three books show a difference in style of presentation. The explanations in Boas are clear and down to earth. The presentation of special functions is characteristic - it is not cast into the framework of self-adjoint (Hermitian) differential operators and Sturm-Liouville equations, as in the other two books. Personally I prefer the latter approach because it shows that special functions arise as eigenfunctions of self-adjoint operators, which ties in nicely with the variational formulation into which most physical theories can be cast. On the whole this book is therefore less formal than that by Riley et al, which is nevertheless not so formal as to put off physics students. Riley et al has clear, thorough and straightforward explanations of the subjects treated. It rigorously adopts a three-stage approach throughout the book: first a heuristic, intuitive introduction, then a formal treatment, and finally one or two examples. This consistent presentation, the layout, and the print quality make the book most attractive. Arfken and Weber's explanations are very much linked into physics, because this book is intended specifically for physicists, whereas the other two cater for a wider audience, though all are suitable for physics degree courses. Arfken and Weber's book treats the subjects in somewhat less detail than the other two, and it is the only book of the three which does not contain answers or hints to selected problems. Arfken and Weber is the most physical, but also the most advanced of the three. Making a choice between these books is not easy. If I had to recommend a maths book to a graduate student, I would probably choose Arfken and Weber because of its more in-depth discussion of advanced material directly related to physics. For an undergraduate university degree course, I would prefer Riley et al because of its clearness of presentation, comprehensiveness and value for money. It contains a thousand pages, there are plenty of exercises with each chapter, and as mentioned above, the layout and print quality are very good. This is a valuable book with great potential use in present-day university physics courses. Furthermore, the book will be useful for graduates too, and researchers will find it useful for looking up material which they have forgotten since their undergraduate days.

Item does not contain fulltext Transport properties of molecular junctions are notoriously expensive to calculate with ab initio methods, primarily due to the semi-infinite electrodes. This has led to the introduction of different approximation schemes for the electrodes. For the most popular metals used in experiments, such as gold, the wide-band limit (WBL) is a particularly efficient choice. In this paper, we investigate the performance of different WBL schemes relative to more sophisticated approaches including the fully self-consistent non-equilibrium Green's function method. We find reasonably good agreement between all schemes for systems in which the molecule (and not the metal-molecule interface) dominates the transport properties. Moreover, our implementation of the WBL requires negligible computational effort compared to the ground-state density-functional theory calculation of a molecular junction. We also present a new approximate but efficient scheme for calculating transport with a finite bias. Provided the voltage drop occurs primarily inside the molecule, this method provides results in reasonable agreement with fully self-consistent calculations.

The cooccurrence matrix is used to analyse echographic video images. However, the size of the speckle, which depends on the transducer characteristics, depth, direction and underlying tissue,1 influences the best choice for the displacement parameter d. Morris2 suggested that an optimal value for d can be obtained in the following way: Firstly, a cooccurrence feature is calculated in the four directions and with different displacements. After this, the mean value of the four angles is calculated and the d at which this mean feature becomes independent of d is estimated. However, because of the different speckle dimensions in axial and lateral direction (expressed by the correlation length), the optimal d in fact is greatly different for these directions. Furthermore, the lateral speckle size is very much depth-dependent1 (200% or more), so the optimal displacement d will also be depth dependent. Finally, it is not sure that all the features will have the same optimal d for a certain speckle size. In this paper the influence of the speckle size on the optimal d is investigated for five cooccurrence features. This investigation might lead to the optimal use of the cooccurrence matrix for detection or differentiation of tissue conditions wich are realted to the effective scattering number density.

Ensemble averaging is generally used for the estimation of Evoked Potentials. This paper deals with the assessment of correction procedures for the time variability of the ensemble components, this time variability reduces the improvement of the signal-to-noise ratio (SNR) by averaging. Evoked potentials were estimated by ensemble averaging, synchronized to a periodic stimulus. It is assumed that VEP-instability is partly caused by time-variability of the evoked potentials. Two time-variate models were used, from which procedures were derived to correct the single VEP-responses prior to ensemble averaging. The models are: (1) variation in response delay (jitter), (2) variable compression/expansion of the time scale of the response (wow). The Spectral Phase Difference method was applied to estimate both the delay time jitter and the wow factor of single responses with respect to a template (conventional ensemble average). The effects of the devised correction on the average VEP waveform and on the SNR of the ensemble were investigated by using data from realistic simulations and from experiments (n = 23) with a number of healthy human volunteers (n = 17). Jitter- and wow-corrections were effective on simulations with time variability due to delay time jitter and time scale distortion (wow), respectively. Both wow- and jitter correction of the single responses improved the SNR of the VEP measurements significantly and to the same amount. A combined wow-jitter approach resulted in significantly better results than the exclusive application of jitter- or wow correction.

The considered causes of variability of visual evoked potentials (VEPs) are additive noise and time variability. The time variability can be modelled in three different ways: 1. time invariant VEP waveform and delay-time "jitter"; 2. time variant VEP waveform, due to 2a. jitter of individual components or 2b. constant VEP waveform and "wow", i.e. expansion or compression of the time scale. The wow model has not been considered so far in the literature. Correction of jitter and/or wow is based on a frequency domain method: the "spectral phase difference" method (SPD). When jitter is present the SPD method is applied in the frequency domain on the single responses, or on a subensemble of a small number of responses. For the wow a new method is proposed where the time scale is logarithmically compressed prior to the calculation of the spectrum. It is shown that the SPD method can also be applied then to estimate the compression factor yielding the wow. The single responses, or the averaged sub-ensembles, can subsequently be corrected by this factor and finally be averaged. Improvement of the precision and accuracy of estimates of both the peak latencies and the peak amplitudes, as well as a comparison between the results of the jitter and wow models, have been reported in a companion paper.

Simulations of the Van der Drift model for polycrystalline growth are described. These simulations have been carried out for conic and cubic crystals and the exponent p describing the growth of the linear monocrystalline domain size has been determined. For both crystal types p=0.4 is found, in accordance with previously obtained mean-field results. Moreover, the angular distribution of surviving crystals as a function of time matches the mean-field result very well.

The conditions for quantitative echography are outlined. First the calibration, data-acquisition and pre-processing are discussed. The preprocessing is necessary to remove the influences of beam-diffraction and focussing, of the instrument setttings, as well as of the attenuation, from the radiofrequency (rf-) signals. The first part of the analysis of echographic data concerns the acoustospectrography, quantifying the frequency dependence of the attenuation and of the backscattering by tissues. The second part of the analysis comprises the assessment of the texture of echographic images (first and second order grey level statistics). The echographic images are processed for improving the detection and subsequent differentiation of pathology (primarily of tumours). Two main categories of processing are distinguished: speckle reduction methods and parametric imaging methods. The quality of these algorithms is assessed by the calculation of the “Lesion Signal-to-Noise-Ratio” (SNRL), which describes the detectability of a lesion by an ideal observer. Parametric imaging comprises the two-dimensional presentation of locally derived acoustic-or image-texture parameters.

We report an in situ transmission electron microscopy (TEM) imaging of grain growth in a Pt nanobridge induced by a high electric current density. The change in morphology at the nanoscale was recorded in real time together with the electrical characterization of the Pt nanobridge. We find a drop in the differential resistance as the voltage across the bridge is increased; TEM inspection shows that this coincides with thermally induced grain growth, indicating that a reduction of grain boundary scattering is the cause of the resistance decrease.