Vacancy clustering effect on the electronic and transport properties of bilayer graphene nanoribbons.

Experimental realizations of two-dimensional materials are hardly free of structural defects such as e.g. vacancies, which, in turn, modify drastically its pristine physical defect-free properties. In this work, we explore effects due to point defect clustering on the electronic and transport properties of bilayer graphene nanoribbons, for AA and AB stacking and zigzag and armchair boundaries, by means of the tight-binding approach and scattering matrix formalism. Evident vacancy concentration signatures exhibiting a maximum amplitude and an universality regardless of the system size, stacking and boundary types, in the density of states around the zero-energy level are observed. Our results are explained via the coalescence analysis of the strong sizeable vacancy clustering effect in the system and the breaking of the inversion symmetry at high vacancy densities, demonstrating a similar density of states for two equivalent degrees of concentration disorder, below and above the maximum value.

Physicians declining patient enrollment in a critical care trial: a case study in thromboprophylaxis.

PURPOSE: To analyze the frequency, rationale and determinants of attending physicians requesting that their eligible patients not be approached for participation in a thromboprophylaxis trial. METHODS: Research personnel in 67 centers prospectively documented eligible non-randomized patients due to physicians declining to allow their patients to be approached. RESULTS: In 67 centers, 3,764 patients were enrolled, but 1,460 eligible patients had no consent encounter. For 218 (14.9 %) of these, attending physicians requested that their patients not be approached. The most common reasons included a high risk of bleeding (31.2 %) related to fear of heparin bioaccumulation in renal failure, the presence of an epidural catheter, peri-operative status or other factors; specific preferences for thromboprophylaxis (12.4 %); morbid obesity (9.6 %); uncertain prognosis (6.4 %); general discomfort with research (3.7 %) and unclear reasons (17.0 %). Physicians were more likely to decline when approached by less experienced research personnel; considering those with[10 years of experience as the reference category, the odds ratios (OR) for physician refusals to personnel without trial experience was 10.47 [95 % confidence interval (CI) 2.19-50.02] and those with less than 10 years experience was 1.72 (95 % CI 0.61-4.84). Physicians in open rather than closed units were more likely to decline (OR 4.26; 95 % CI 1.27-14.34). Refusals decreased each year of enrollment compared to the pilot phase. CONCLUSIONS: Tracking, analyzing, interpreting and reporting the rates and reasons for physicians declining to allow their patients to be approached for enrollment provides insights into clinicians' concerns and attitudes to trials. This information can encourage physician communication and education, and potentially enhance efficient recruitment.

The electronic properties of graphene and graphene ribbons under simple shear strain.

A tight-binding model is used to study the energy band of graphene and graphene ribbon under simple shear strain. The ribbon consists of lines of carbon atoms in an armchair or zigzag orientation where a simple shear strain is applied in the x-direction keeping the atomic distances in the y-direction unchanged. Such modification in the lattice gives an energy band that differs in several aspects from the one without any shear and with pure shear. The changes in the spectrum depend on the line displacement of the ribbon, and also on the modified hopping parameter. It is also shown that this simple shear strain tunes the electronic properties of both graphene and graphene ribbon, opening and closing energy gaps for different displacements of the system. The modified density of states is also shown.

Model for erosion-deposition patterns.

We investigate through computational simulations with a pore network model the formation of patterns caused by erosion-deposition mechanisms. In this model, the geometry of the pore space changes dynamically as a consequence of the coupling between the fluid flow and the movement of particles due to local drag forces. Our results for this irreversible process show that the model is able to reproduce typical natural patterns caused by well-known erosion processes. Moreover, we observe that, within a certain range of porosity values, the grains form clusters that are tilted with respect to the horizontal with a characteristic angle. We compare our results to recent experiments for granular material in flowing water and show that they present a satisfactory agreement.

First detection of Corynebacterium ulcerans producing a diphtheria-like toxin in a case of human with pulmonary infection in the Rio de Janeiro metropolitan area, Brazil.

The frequency and severity of human infections associated with Corynebacterium ulcerans appear to be increasing in different countries. Here, we describe the first C. ulcerans strain producing a diphtheria-like toxin isolated from an elderly woman with a fatal pulmonary infection and a history of leg skin ulcers in the Rio de Janeiro metropolitan area.

First detection of Corynebacterium ulcerans producing a diphtheria-like toxin in a case of human with pulmonary infection in the Rio de Janeiro metropolitan area, Brazil

The frequency and severity of human infections associated with Corynebacterium ulcerans appear to be increasing in different countries. Here, we describe the first C. ulcerans strain producing a diphtheria-like toxin isolated from an elderly woman with a fatal pulmonary infection and a history of leg skin ulcers in the Rio de Janeiro metropolitan area.

Structure, normal mode spectra, and mixing of a binary system of charged particles confined in a parabolic trap.

We study the mixing of two different kinds of particles, having different charge and/or mass, interacting through a pure Coulomb potential, and confined in a parabolic trap. The structure of the cluster and its normal mode spectrum are analyzed as a function of the ratio of the charges (mass ratio) of the two types of particles. We show that particles are not always arranged in a shell structure. Mixing of the particles goes hand in hand with a large number of metastable states. The normal modes of the system are obtained, and we find that some of the special modes can be tuned by varying the ratio between the charges (masses) of the two species. The degree of mixing of the two type of particles is summarized in a phase diagram, and an order parameter that describes quantitatively the mixing between particles is defined.

Nanopercolation.

We investigate through direct molecular mechanics calculations the geometrical properties of hydrocarbon mantles subjected to percolation disorder. We show that the structures of mantles generated at the critical percolation point have a fractal dimension df approximately 2.5. In addition, the solvent access surface As and volume Vs of these molecules follow power-law behavior, As approximately L(alphaA) and Vs approximately L(alphaV), where L is the system size, and with both exponents alphaA and alphaV being significantly dependent on the radius of the accessing probing molecule, r(p). Our results from extensive simulations with two distinct microscopic topologies (i.e., square and honeycomb) indicate the consistency of the statistical analysis and confirm the self-similar characteristic of the percolating hydrocarbons. Due to their highly branched topology, this new class of disordered molecules can be of potential use in a variety of practical applications.

Majority-vote model on a random lattice.

The stationary critical properties of the isotropic majority vote model on random lattices with quenched connectivity disorder are calculated by using Monte Carlo simulations and finite size analysis. The critical exponents gamma and beta are found to be different from those of the Ising and majority vote on the square lattice model and the critical noise parameter is found to be q(c) =0.117+/-0.005 .

Memory effects on the statistics of fragmentation.

We investigate through extensive molecular dynamics simulations the fragmentation process of two-dimensional Lennard-Jones systems. After thermalization, the fragmentation is initiated by a sudden increment to the radial component of the particles' velocities. We study the effect of temperature of the thermalized system as well as the influence of the impact energy of the "explosion" event on the statistics of mass fragments. Our results indicate that the cumulative distribution of fragments follows the scaling ansatz F(m) proportional to m(1-alpha)exp-(m/m(0))(gamma), where m is the mass, m(0) and gamma are cutoff parameters, and alpha is a scaling exponent that is dependent on the temperature. More precisely, we show clear evidence that there is a characteristic scaling exponent alpha for each macroscopic phase of the thermalized system, i.e., that the nonuniversal behavior of the fragmentation process is dictated by the state of the system before it breaks down.

Statistics of the critical percolation backbone with spatial long-range correlations.

We study the statistics of the backbone cluster between two sites separated by distance r in two-dimensional percolation networks subjected to spatial long-range correlations. We find that the distribution of backbone mass follows the scaling ansatz, P(M(B)) approximately M(-(alpha+1))(B)f(M(B)/M(0)), where f(x)=(alpha+etax(eta))exp(-x(eta)) is a cutoff function and M0 and eta are cutoff parameters. Our results from extensive computational simulations indicate that this scaling form is applicable to both correlated and uncorrelated cases. We show that the exponent alpha can be directly related to the fractal dimension of the backbone d(B), and should therefore depend on the imposed degree of long-range correlations.

Tetraplegic ambulation with the ORLAU swivel walker: a case report.

The ORLAU Swivel Walker which had previously been used by children with spina bifida. has been modified so that it is now being successfully used by spinal cord paralysed patients. This is a case study of a C7 traumatic tetraplegic patient who has used the ORLAU swivel walker for 5 years.

Scaling behavior in a proportional voting process.

We perform a statistical analysis on the proportional elections held in Brazil in October 1998. We show that the distribution of votes among candidates for the whole country follows a power law N(v) is proportional to v(-alpha), with alpha=1.00+/-0.02, extending over two orders of magnitude. The voting distributions for several states of the federation also display scale-invariant behavior with alpha approximately equal to 1. We argue that this particular voting system can be modeled as a typical multiplicative process in which the choice of the candidate is governed by a product of probabilities.

[Are the spontaneous coronary recanalization and the coronary collateral circulation really important in the left ventricular preservation in acute myocardial infarct?]. / A recanalização coronária espontânea e a circulação colateral coronária são realmente importantes na preservação ventricular esquerda no infarto agudo do miocárdio?

PURPOSE: To determine if maintenance of residual blood flow to culprit coronary artery in acute myocardial infarction is important in preserving left ventricular systolic function. METHODS: Prospective study of 63 consecutive survivors of acute myocardial infarction in the prethrombolytic era that were submitted to cinecoronary angiography and 30 degrees RAO left ventriculography on the 4th week. Culprit coronary artery patency and collateral circulation were correlated with global and segmental left ventricular contractility. RESULTS: Spontaneous coronary recanalization correlated significantly with better left ventricular systolic function only in patients with anterior wall myocardial infarction. This relationship was stronger with segmental than with global contractility. Besides, it was seen that absence of recanalization of pre-septal left anterior descending coronary artery occlusion resulted in significantly worse global and segmental left ventricular systolic function than post-septal occlusion, resulting in left ventricular aneurysm in all patients (2/3 of recanalized patients versus 1/3 of post-septal occlusions). Collateral circulation to culprit coronary artery correlated significantly with better global and segmental left ventricular contractility only in patients with inferior wall myocardial infarction. CONCLUSION: In acute anterior wall myocardial infarction spontaneous coronary artery recanalization is associated with better global and segmental left ventricular systolic function, specially if the occlusion is of pre-septal localization, while collateral circulation is not related to better contractility. In acute inferior wall myocardial infarction one sees the reverse.

[R-R variability in acute anterior infarct after thrombolytic therapy]. / Variabilidade de R-R no infarto agudo anterior após a terapêutica trombolítica.

PURPOSE: To analyse the effects of thrombolysis on the integrity of the autonomic nervous system, in patient with acute myocardial infarction (AMI) of the anterior wall, using the determination of the heart rate variability. METHODS: We prospectively evaluated the R-R variability of the 31 consecutive patients with anterior AMI submitted to coronary thrombolysis (25 males; mean age 59 +/- 14 years) from Holter tapes. An algorithm in a 286 computer program was used for heart rate variability (HRV). With this system, R-R variations during sinus rhythm and for a five consecutive minutes periods was determined. The results were expressed as the mean of the total determined periods; the standard deviation of the mean of all determined periods and the mean of the standard deviation. The reperfusion criteria was the early enzymatic rise of the CKMB activity levels (< or = 12 h) combined with a 50% or more reduction in the ST segment elevation within the first hour after thrombolytic therapy and the presence of an accelerated idioventricular rhythm at the same time. The reperfused group (group 1 = 16 patients) and non-reperfused group (group 2 = 15 patients) were compared in terms of R-R variability. RESULTS: Mean R-R: group 1 = 716 +/- 84 ms (540-820 ms); group 2 = 595 +/- 115 ms (390-870 ms)-p < 0.02. ms (34-92 ms); group 2 = 50 +/- 14 ms (23-77 ms)-p < 0.01. HRV 50 ms: group 1 = 2 patients; group 2 = 5 patients. Means SD of the R-R: group 1 = 44 +/- 14 ms (26-65 ms); group 2 = 39 +/- 17 ms (19-69 ms)-p: ns. CONCLUSION: Patients with anterior AMI and thrombolytic therapy demonstrate greater HRV; this finding suggested better integrity of the autonomic nervous system, with possible effects on prognosis.

[Polymorphic ventricular tachycardia. Analysis of the onset of the episodes]. / Taquicardia ventricular polimórfica. Análise do início dos surtos.

PURPOSE: To analyze the spontaneous onset of events for polymorphous ventricular tachycardia, to determine the importance of this parameter in the clinical and electrophysiologic context. METHODS: We evaluated 124 modes of onset of polymorphous ventricular tachycardias recorded by 24 hr of continuous ECG monitoring in 6 patients. Four patients were using quinidine and diuretics, and two patients only diuretics. We determined the two preceding cycle in milliseconds from the initiating events and also the induced cycle (cycles A, B and C). Careful analyses of T and U waves alternans and QT ou QTU intervals inside and outside the episodes of tachycardia. RESULTS: In 105 episodes (84%) the events were pause-dependent; in 12 episodes (10%) they occurred without pauses but after a ventricular fusion and in 7 episodes (6%) also without pauses but with sudden cycle (C) shortening (R on T phenomena). The pause-dependent episodes were only seen in patients using quinidine with the association of diuretics and non-pause related episodes were registered in patients using diuretics. All patients had prolonged QTU intervals outside the episodes. There were a linear correlation (r = 0.865) between the amplitude of the U waves of the cycles C and duration of cycles A and B, in pause-dependent episodes. CONCLUSION: The contribution of this study is that: the analyses of the spontaneous onset of polymorphous ventricular tachycardia can allow the differentiation of typic forms of torsades des de pointes (pause-dependent) and other atipic forms. The former type occurred probably as a result of EADs provoking triggered rhythms. The latter could be better explained as polymorphous ventricular tachycardia due to reentry mechanisms or enhanced automatic focus. Only the tipic forms should be acutely benefited with regularization of cardiac cycles with cardiac pacing.