Phenotype constrains the vocal tract in the most dimorphic mammal, the southern elephant seal

The study of mammal acoustic communication was revolutionized by the application of the source-filter theory, originally developed for human speech. The theory states that the vocal tract is constrained by body anatomy and, therefore, creates a structural link between phenotype and acoustic formants, providing a basis for honest signalling. The phenotype-formants link was validated in many species, but the phenotype-vocal tract link was rarely assessed. We used 2D videogrammetry to estimate the vocal tract length of wild southern elephant seal males (Mirounga leonina Linnaeus, 1758) during their normal vocalization behaviour. We showed that: 1) the vocal tract can be measured non-invasively in a wild large mammal; 2) the vocal tract depends on the structural phenotype (age, body length, and skull size); 3) the nasal tract is more related to the structural phenotype than the buccal tract; 4) the dependence on size, and body length in particular, is stronger than the dependence on age. All together, the phenotypic constraint on vocal tract provides the anatomical basis for honest signalling in elephant seals.

Complex band structure with non-orthogonal basis set: analytical properties and implementation in the SIESTA code

The complex band structure (CBS), although not directly observable, determines many properties of a material where the periodicity is broken, such at surfaces, interfaces and defects. Furthermore, its knowledge helps in the interpretation of electronic transport calculations and in the study of topological materials. Here we extend the transfer matrix method, often used to compute the complex bands, to electronic structures constructed using an atomic non-orthogonal basis set. We demonstrate that when the overlap matrix is not the identity, the non-orthogonal case, spurious features appear in the analytic continuation of the band structure to the complex plane. The properties of these are studied both numerically and analytically and discussed in the context of existing literature. Finally, a numerical implementation to extract the CBS from periodic calculations carried out with the density functional theory codesiestais presented. This is constructed as a simple post-processing tool, and it is therefore amenable to high-throughput studies of insulators and semiconductors.

Overlap between marine predators and proposed Marine Managed Areas on the Patagonian Shelf

Static (fixed-boundary) protected areas are key ocean conservation strategies, and marine higher predator distribution data can play a leading role toward identifying areas for conservation action. The Falkland Islands are a globally significant site for colonial breeding marine higher predators (i.e., seabirds and pinnipeds). However, overlap between marine predators and Falkland Islands proposed Marine Managed Areas (MMAs) has not been quantified. Hence, to provide information required to make informed decisions regarding the implementation of proposed MMAs, our aims were to objectively assess how the proposed MMA network overlaps with contemporary estimates of marine predator distribution. We collated tracking data (1999-2019) and used a combination of kernel density estimation and model-based predictions of spatial usage to quantify overlap between colonial breeding marine predators and proposed Falkland Islands MMAs. We also identified potential IUCN Key Biodiversity Areas (pKBAs) using (1) kernel density based methods originally designed to identify Important Bird and Biodiversity Areas (IBAs) and (2) habitat preference models. The proposed inshore MMA, which extends three nautical miles from the Falkland Islands, overlapped extensively with areas used by colonial breeding marine predators. This reflects breeding colonies being distributed throughout the Falklands archipelago, and use being high adjacent to colonies due to central-place foraging constraints. Up to 45% of pKBAs identified via kernel density estimation were located within the proposed MMAs. In particular, the proposed Jason Islands Group MMA overlapped with pKBAs for three marine predator species, suggesting it is a KBA hot spot. However, tracking data coverage was incomplete, which biased pKBAs identified using kernel density methods, to colonies tracked. Moreover, delineation of pKBA boundaries were sensitive to the choice of smoothing parameter used in kernel density estimation. Delineation based on habitat model predictions for both sampled and unsampled colonies provided less biased estimates, and revealed 72% of the Falkland Islands Conservation Zone was likely a KBA. However, it may not be practical to consider such a large area for fixed-boundary management. In the context of wide-ranging marine predators, emerging approaches such as dynamic ocean management could complement static management frameworks such as MMAs, and provide protection at relevant spatiotemporal scales.

Unveiling phonons in a molecular qubit with four-dimensional inelastic neutron scattering and density functional theory

Phonons are the main source of relaxation in molecular nanomagnets, and different mechanisms have been proposed in order to explain the wealth of experimental findings. However, very limited experimental investigations on phonons in these systems have been performed so far, yielding no information about their dispersions. Here we exploit state-of-the-art single-crystal inelastic neutron scattering to directly measure for the first time phonon dispersions in a prototypical molecular qubit. Both acoustic and optical branches are detected in crystals of [VO(acac)[Formula: see text]] along different directions in the reciprocal space. Using energies and polarisation vectors calculated with state-of-the-art Density Functional Theory, we reproduce important qualitative features of [VO(acac)[Formula: see text]] phonon modes, such as the presence of low-lying optical branches. Moreover, we evidence phonon anti-crossings involving acoustic and optical branches, yielding significant transfers of the spin-phonon coupling strength between the different modes.

Male and female pups of the highly sexually dimorphic northern elephant seal (Mirounga angustirostris) differ slightly in body size

In mammals, males generally are larger than females, though such sexual-size differences have been documented primarily in adults and are relatively poorly known in early life. We studied sexual-size differences in pups of the northern elephant seal (Mirounga angustirostris (Gill, 1866)), which in adulthood is one of the most sexually dimorphic mammals. We studied body size at birth and weaning, at Islas San Benito, Mexico, at the southernmost limit of the species’ breeding range. Males were 10% heavier and 2% longer than females at birth. Sexes did not differ significantly in either measure of body size at weaning, although males were slightly heavier (4%) and longer (1%) than females. Neither growth rate nor suckling duration differed between the sexes. In previous studies in California, USA, pups at weaning were heavier than in our study, and males were heavier than females. These differences may reflect ecological, temporal, or life-history differences across populations. The modest difference in sexual-size dimorphism early in life in this species compared with the great difference in adulthood likely reflects multiple selective forces, including constraints on neonatal size set by body size of females, and the weakness of sexual selection at that stage of life.

Demographic histories and genetic diversity across pinnipeds are shaped by human exploitation, ecology and life-history

A central paradigm in conservation biology is that population bottlenecks reduce genetic diversity and population viability. In an era of biodiversity loss and climate change, understanding the determinants and consequences of bottlenecks is therefore an important challenge. However, as most studies focus on single species, the multitude of potential drivers and the consequences of bottlenecks remain elusive. Here, we combined genetic data from over 11,000 individuals of 30 pinniped species with demographic, ecological and life history data to evaluate the consequences of commercial exploitation by 18th and 19th century sealers. We show that around one third of these species exhibit strong signatures of recent population declines. Bottleneck strength is associated with breeding habitat and mating system variation, and together with global abundance explains much of the variation in genetic diversity across species. Overall, bottleneck intensity is unrelated to IUCN status, although the three most heavily bottlenecked species are endangered. Our study reveals an unforeseen interplay between human exploitation, animal biology, demographic declines and genetic diversity.

Historical hunting has caused documented declines in pinnipeds, but the extent to which hunting caused genetic bottlenecks among species was unknown. Here, the authors show evidence of severe bottlenecks in several pinniped species, particularly those that breed on land.

Current-induced changes of migration energy barriers in graphene and carbon nanotubes

An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.

The image charge effect and vibron-assisted processes in Coulomb blockade transport: a first principles approach

We present a combination of density functional theory and of both non-equilibrium Green's function formalism and a Master equation approach to accurately describe quantum transport in molecular junctions in the Coulomb blockade regime. We apply this effective first-principles approach to reproduce the experimental results of Perrin et al., [Nat. Nanotechnol., 2013, 8, 282] for the transport properties of a Au-(Zn)porphyrin-Au molecular junction. We demonstrate that energy level renormalization due to the image charge effect is crucial to the prediction of the current onset in the current-voltage, I-V, curves as a function of electrode separation. Furthermore, we show that for voltages beyond that setting the current onset, the slope of the I-V characteristics is determined by the interaction of the charge carriers with molecular vibrations. This corresponds to current-induced local heating, which may also lead to an effective reduced electronic coupling. Overall our scheme provides a fully ab initio description of quantum transport in the Coulomb blockade regime in the presence of electron-vibron coupling.

Tailoring highly conductive graphene nanoribbons from small polycyclic aromatic hydrocarbons: a computational study

Pyrene, the smallest two-dimensional mesh of aromatic rings, with various terminal thiol substitutions, has been considered as a potential molecular interconnect. Charge transport through two terminal devices has been modeled using density functional theory (with and without self interaction correction) and the non-equilibrium Green's function method. A tetra-substituted pyrene, with dual thiol terminal groups at opposite ends, has been identified as an excellent candidate, owing to its high conductance, virtually independent of bias voltage. The two possible extensions of its motif generate two series of graphene nanoribbons, with zigzag and armchair edges and with semimetallic and semiconducting electron band structure, respectively. The effects related to the wire length and the bias voltage on the charge transport have been investigated for both sets. The conductance of the nanoribbons with a zigzag edge does not show either length or voltage dependence, owing to an almost perfect electron transmission with a continuum of conducting channels. In contrast, for the armchair nanoribbons a slow exponential attenuation of the conductance with the length has been found, due to their semiconducting nature.

Time-dependent electron transport through a strongly correlated quantum dot: multiple-probe open-boundary conditions approach

We present a time-dependent study of electron transport through a strongly correlated quantum dot, which combines adiabatic lattice density functional theory in the Bethe ansatz local-density approximation (BALDA) to the Hubbard model, with the multiple-probe battery method for open-boundary simulations in the time domain. In agreement with the recently proposed dynamical picture of Coulomb blockade, a characteristic driven regime, defined by regular current oscillations, is demonstrated for a certain range of bias voltages. We further investigate the effects of systematically improving the approximation for the electron-electron interaction at the dot site (going from non-interacting, through Hartree-only to adiabatic BALDA) on the transmission spectrum and the I-V characteristics. In particular, a negative differential conductance is obtained at large bias voltages and large Coulomb interaction strengths. This is attributed to the combined effect of the electron-electron interaction at the dot and the finite bandwidth of the electrodes.

Fine-scale population structure of blue whale wintering aggregations in the Gulf of California

Population differentiation in environments without well-defined geographical barriers represents a challenge for wildlife management. Based on a comprehensive database of individual sighting records (1988–2009) of blue whales from the winter/calving Gulf of California, we assessed the fine-scale genetic and spatial structure of the population using individual-based approaches. Skin samples of 187 individuals were analyzed for nine microsatellite loci. A single population with no divergence among years and months and no isolation by distance (Rxy = 0.1–0.001, p>0.05) were found. We ran two Bayesian clustering methods using Structure and Geneland softwares in two different ways: 1) a general analysis including all individuals in which a single cluster was identified with both softwares; 2) a specific analysis of females only in which two main clusters (Loreto Bay and northern areas, and San Jose-La Paz Bay area) were revealed by Geneland program. This study provides information indicating that blue whales wintering in the Gulf of California are part of a single population unit and showed a fine-scale structure among females, possibly associated with their high site fidelity, particularly when attending calves. It is likely that the loss of genetic variation is minimized by male mediated gene flow, which may reduce the genetic drift effect. Opportunities for kin selection may also influence calf survival and, in consequence, have a positive impact on population demography in this small and endangered population.

Giant resistance change across the phase transition in spin-crossover molecules

The electronic origin of a large resistance change in nanoscale junctions incorporating spin-crossover molecules is demonstrated theoretically by using a combination of density functional theory and the nonequilibrium Green's function method for quantum transport. At the spin-crossover phase transition, there is a drastic change in the electronic gap between the frontier molecular orbitals. As a consequence, when the molecule is incorporated in a two-terminal device, the current increases by up to 4 orders of magnitude in response to the spin change. This is equivalent to a magnetoresistance effect in excess of 3000%. Since the typical phase transition critical temperature for spin-crossover compounds can be extended to well above room temperature, spin-crossover molecules appear as the ideal candidate for implementing spin devices at the molecular level.

Persistent current and Drude weight for the one-dimensional Hubbard model from current lattice density functional theory

The Bethe ansatz local density approximation (LDA) to lattice density functional theory (LDFT) for the one-dimensional repulsive Hubbard model is extended to current-LDFT (CLDFT). The transport properties of mesoscopic Hubbard rings threaded by a magnetic flux are then systematically investigated by this scheme. In particular we present calculations of ground state energies, persistent currents and Drude weights for both a repulsive homogeneous and a single impurity Hubbard model. Our results for the ground state energies in the metallic phase compare favorably well with those obtained with numerically accurate many-body techniques. Also the dependence of the persistent currents on the Coulomb and the impurity interaction strength, and on the ring size are all well captured by LDA-CLDFT. Our study demonstrates the value of CLDFT in describing the transport properties of one-dimensional correlated electron systems. As its computational overheads are rather modest, we propose this method as a tool for studying problems where both disorder and interaction are present.

The search for a spin crossover transition in small sized π-conjugated molecules: a Monte Carlo study

The spin crossover transition in π-conjugated polymers is a complex phenomenon involving a balance between Coulomb interaction and collective lattice distortions. We explore such a transition with a minimal electronic model comprising a Hubbard-U on-site repulsive potential and both electron-phonon and hyperfine interactions. The model is then solved numerically for small molecules at finite temperature by Monte Carlo methods in the search for the spin crossover. This is done at the mean field level in the Hubbard-U interaction at half filling. We demonstrate that for a certain region of the parameter space there is a spin crossover, where the system transits from a low-spin to a high-spin state as the temperature increases. In close analogy to standard spin crossover in divalent magnetic molecules such a transition is entropy driven, with both the spin and the vibrational contributions to the entropy being relevant. Such a transition is practically unaffected by the hyperfine interaction, which only plays a minor role in determining the electronic properties.

Electric field control of valence tautomeric interconversion in cobalt dioxolene

We demonstrate that the critical temperature for valence tautomeric interconversion in cobalt dioxolene complexes can be significantly changed when a static electric field is applied to the molecule. This is achieved by effectively manipulating the redox potential of the metallic acceptor forming the molecule. Importantly, our accurate density functional theory calculations demonstrate that already a field of 0.1  V/nm, achievable in Stark spectroscopy experiments, can produce a change in the critical temperature for the interconversion of 20 K. Our results indicate a new way for switching on and off the magnetism in a magnetic molecule. This offers the unique chance of controlling magnetism at the atomic scale by electrical means.

Computational modeling of a carbon nanotube-based DNA nanosensor

During the last decade the design of biosensors, based on quantum transport in one-dimensional nanostructures, has developed as an active area of research. Here we investigate the sensing capabilities of a DNA nanosensor, designed as a semiconductor single walled carbon nanotube (SWCNT) connected to two gold electrodes and functionalized with a DNA strand acting as a bio-receptor probe. In particular, we have considered both covalent and non-covalent bonding between the DNA probe and the SWCNT. The optimized atomic structure of the sensor is computed both before and after the receptor attaches itself to the target, which consists of another DNA strand. The sensor's electrical conductance and transmission coefficients are calculated at the equilibrium geometries via the non-equilibrium Green's function scheme combined with the density functional theory in the linear response limit. We demonstrate a sensing efficiency of 70% for the covalently bonded bio-receptor probe, which drops to about 19% for the non-covalently bonded one. These results suggest that a SWCNT may be a promising candidate for a bio-molecular FET sensor.

Electronic transport calculations for rough interfaces in Al, Cu, Ag, and Au

We present results of electronic structure and transport calculations for metallic interfaces, based on density functional theory and the non-equilibrium Green's function method. Starting from the electronic structure of smooth Al, Cu, Ag, and Au interfaces, we study the effects of different kinds of interface roughness on the transmission coefficient and the I-V characteristic. In particular, we compare prototypical interface distortions, including vacancies and metallic impurities.

Switching a single spin on metal surfaces by a STM Tip: Ab Initio studies

The exchange coupling between single 3d magnetic adatoms (Cr, Mn, Fe, and Co) adsorbed on a Cu(001) surface and a Cr STM tip is studied with ab initio calculations. We demonstrate that the spin direction of single adatoms can be controlled by varying the tip-substrate distance, and the sign of the exchange energy is determined by the competition of the direct and the indirect interactions between the tip and the adatom. Based on the spin-dependent transport calculations, we find a magnetoresistance of about 70% at short tip-substrate distances.

Exchange parameters from approximate self-interaction correction scheme

The approximate atomic self-interaction correction (ASIC) method to density functional theory is put to the test by calculating the exchange interaction for a number of prototypical materials, critical to local exchange and correlation functionals. ASIC total energy calculations are mapped onto a Heisenberg pairwise interaction and the exchange constants J are compared to those obtained with other methods. In general the ASIC scheme drastically improves the band structure, which for almost all the cases investigated resemble closely available photoemission data. In contrast the results for the exchange parameters are less satisfactory. Although ASIC performs reasonably well for systems where the magnetism originates from half-filled bands, it suffers from similar problems than those of local density approximation for other situations. In particular, the exchange constants are still overestimated. This reflects a subtle interplay between exchange and correlation energy, not captured by the ASIC.

Efficient atomic self-interaction correction scheme for nonequilibrium quantum transport

Density-functional theory calculations of electronic transport based on local exchange and correlation functionals contain self-interaction errors. As a consequence, insulating molecules in weak contact with metallic electrodes erroneously form highly conducting junctions. Here we present a fully self-consistent and still computationally undemanding self-interaction correction scheme that overcomes these limitations. The method is implemented in the transport code SMEAGOL and applied to the prototypical case of benzene molecules and gold electrodes. The Kohn-Sham highest occupied molecular orbital now reproduces closely the negative of the molecular ionization potential and is moved away from the gold Fermi energy. This leads to a drastic reduction of the low-bias current in much better agreement with experiments.

Effect of the continuity of the π conjugation on the conductance of ruthenium-octene-ruthenium molecular junctions

The conductance of a family of ruthenium-octene-ruthenium molecular junctions with different pi conjugation are investigated using a fully self-consistent ab initio approach which combines the nonequilibrium Green's function formalism with density functional theory. Our calculations demonstrate that the continuity of the pi conjugation in the contact region as well as along the molecular backbone affects the junction conductance significantly, showing the advantage of using the ruthenium-carbon double bond as the linkage of conjugated organic molecules.

Having a big nose: structure, ontogeny, and function of the elephant seal proboscis

The proboscis of male elephant seals ( Mirounga Gray, 1827) has been suggested as an example of a secondary sexual trait since Darwin. There has been much speculation about its social function (e.g., optical signal of breeding status, amplification of vocalizations, cue for female choice). However, it has never been studied in detail, probably because its fleshy nature makes measurement difficult. In this paper, we employ photogrammetry to measure the proboscis and facial morphology of a large sample of wild, unrestrained, displaying male southern elephant seals ( Mirounga leonina (L., 1758)). We describe ontogeny and allometry of the proboscis and analyze current phenotypic selection pressures on proboscis traits. We discuss the potential role of the proboscis in optical and acoustic signaling of male resource-holding potential and status. We demonstrate that proboscis size is positively correlated with age and body size independently, and that it is currently under a positive sexual selection pressure when the effect of selection on body size is removed. We suggest that selection on proboscis size is functionally related to the emission of agonistic vocalizations.

Conductance oscillations in zigzag platinum chains

Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties of monatomic platinum chains, sandwiched between platinum electrodes. First, we demonstrate that the most stable atomic configuration corresponds to a zigzag arrangement that gradually straightens as the chains are stretched. Second, we find that the averaged conductance shows slight parity oscillations with the number of atoms in the chain. Additionally, the conductance of chains of fixed oscillates as the end atoms are pulled apart, due to the gradual closing and opening of conductance channels as the chain straightens.

Self-interaction errors in density-functional calculations of electronic transport

All density-functional calculations of single-molecule transport to date have used continuous exchange-correlation approximations. The lack of derivative discontinuity in such calculations leads to the erroneous prediction of metallic transport for insulating molecules. A simple and computationally undemanding atomic self-interaction correction (SIC) opens conduction gaps in I-V characteristics that otherwise are predicted metallic, as in the case of the prototype Au/ditholated-benzene/Au junction.

Lattice distortion effects on the magnetostructural phase transition of MnAs

We present a systematic experimental and theoretical study of the first-order phase transition of epitaxially grown MnAs thin films under biaxial tensile stress. Our results give direct information on the dependence of the phase-transition temperature of MnAs films on the lattice parameters. We demonstrate that an increase of the lattice constant in the hexagonal plane raises the phase-transition temperature (T(p)), while an increase of the perpendicular lattice constant lowers T(p). The results of calculations based on density functional theory are in good agreement with the experimental ones. Our findings open exciting prospects for magneto-mechanical devices, where the critical temperature for ferromagnetism can be engineered by external stress.

Ferromagnetism driven by intrinsic point defects in HfO(2)

In view of recent experimental reports of unexpected ferromagnetism in HfO(2) thin films, we carried out first-principles investigations looking for magnetic order possibly brought about by the presence of small concentrations of intrinsic point defects. Ab initio electronic structure calculations using density functional theory show that isolated cation vacancy sites in HfO(2) lead to the formation of high-spin defect states. Furthermore these appear to be ferromagnetically coupled with a rather short range magnetic interaction, resulting in a ferromagnetic ground state for the whole system. More interestingly, the occurrence of these high-spin states and ferromagnetism is in the low symmetry monoclinic phase of HfO(2). This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.

Measures of breeding inequality: a case study in southern elephant seals

Inequality in distribution of resources is a key aspect of evolutionary biology particularly in relation to distribution of mates and copulations. Notwithstanding its important role, inequality is not easily defined, and its measurement is complicated by theoretical and methodological issues. Although the formal treatment of inequality has been mostly limited to the evolution of lek mating system, a methodologically correct approach to measurement of inequality is generally valid for the study of any kind of mating system. In this paper, we analyze inequality in a large set of southern elephant seal (Mirounga leonina) harems. The observed distribution of fertilizations was significantly different from both the expected distribution with equal shares of resources and the expected distribution with equal propensities to acquire resources. We calculate and compare various measures of inequality, observing a wide variation particularly among unbounded and bounded indices. We check the effect of choosing a specific measure of inequality by considering the effect of two aspects of harem socionomy, the number of females in the harem (i.e., the total amount of resources to be shared) and the number of males associated with the harem (i.e., the number of competitors). The choice of a specific measure of inequality had a strong impact on the results obtained and should be considered a critical step in every study of functional and evolutionary correlates of inequality. Unbounded indices showed a strong relationship with both harem size and number of males, while no effect was evident in the analysis of bounded indices. This demonstrates that, in this species, the despotism of the mating system remains high even in large harems and with many competitors, i.e., the worst conditions for monopolization.

Ab initio transport theory for digital ferromagnetic heterostructures

We present a theoretical density functional study of the electronic, magnetic, and transport properties of digital ferromagnetic heterostructures, obtained by delta doping GaAs with Mn. In the absence of intrinsic donors these systems have a half metallic density of states, with an exchange interaction much stronger than that of a random alloy with the same Mn concentration. Our ab initio ballistic transport calculations show that the carriers at the Fermi energy are strongly confined within a few monolayers around the MnAs plane. This strong confinement is responsible for the large exchange coupling and the two-dimensional half metallic behavior.

[Role of high resolution color-Doppler US of the sentinel node in patients with stage I melanoma]

PURPOSE

The aims of the present work are to assess the diagnostic accuracy of high resolution color Doppler ultrasound (US) of the sentinel node (SN) in patients with cutaneous melanoma skin at stage I. The US findings of nodal involvement could spare the patient a surgical step (selective lymphaderectomy) allowing them to undergo radical lymphadenectomy directly.

MATERIAL AND METHODS

From November 1998 to November 2000 94 patients (mean age 52.7 years) underwent lymphoscintigraphy in order to mark the SN site on their skin. An US scan (112 lymphatic basins) was performed within 24 hours with a 10-13 MHz electronic linear probe with color-power-Doppler (Esaote AU5 Idea Scanner, Genoa, Italy). The sonographic features we analysed were: shape (roundness index), hilum displacement, intranodal heterogenicity, eccentric cortical thickness, extranodal invasion, vessel irregularity.

RESULTS

26 nodes showed US findings consistent with malignant involvement, 86 were negative. All the nodes were surgically removed and controlled by histology. Sensitivity and specificity of US scanning were 89.4% and 90.3%, the positive and negative predictive values 65.3% and 97.6%, respectively. US correctly identified the involved SN in 15,1% cases, so that 17 patients could have avoided the selective lymphadenectomy

CONCLUSION

Preoperative lymphoscintigraphy and high-resolution color-Doppler US scanning constitute a useful diagnostic tool in identifying the metastatic SN, with a low margin of error. False negatives were technically induced, even using the more recent scanners, by the low US probe resolution, unable to recognise metastatic microdeposits. The two most reliable parameters in identifying involved lymphnodes were the roundness index and the absence of hilar echo. The advent of technologically more advanced probes should allow better spatial resolution and assessment of lymph node vascularization, enabling diagnosis of metastasis measuring less than 2 mm in diameter.

Fractional quantum conductance in carbon nanotubes

Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].