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In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in threedimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks. [ABSTRACT FROM AUTHOR]

Using a linear array of voltage electrodes with a separation of several micrometers on a 20 nm thick and 30 μm long multigraphene sample, we show that the measured resistance does not follow the usual length dependence according to Ohm's law. The deviations can be quantitatively explained taking into account Sharvin-Knudsen formula for ballistic transport. This allows us to obtain without free parameters the mean free path of the carriers in the sample at different temperatures. In agreement with recently reported values obtained with a different experimental method, we obtain that the carrier mean free path is of the order of ∼2 μm with a mobility μ ∼ 107 cm2V-1 s-1. The results indicate that the usual Ohm's law is not adequate to calculate the absolute resistivity of mesoscopic graphite samples. [ABSTRACT FROM AUTHOR]

Presents a study which examined the magnetic forces involved in the interaction between a single-domain tip and the sample surface magnetic domains using the atomic force microscope (AFM) technique. Influence of the experimental conditions on the performance of AFM as a magnetic profiling device; Description of how to obtain images in the magnetic version of AFM; Results of the study.

Presents a study that investigated the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian. Two-time correlation function of the magnetization; Temporal evolution; Analysis of the correlation function and the spectrum in terms of macroscopic quantum coherence.

Presents information on a study which examined the magnetic behavior of iron-copper (FeCu) alloys. Electron linearized augmented plane-wave calculations of band structures; Density of states for FeCu alloys; Conclusion.

Focuses on a study which performed Monte Carlo simulations on 2D circular Ising clusters to study the distribution of the magnetization within the cluster, as well as the magnetization reversal process when an applied external field is suddenly changed. Methodology of the study; Results and discussion; Conclusion.

We have measured the temperature and magnetic field dependence of the Hall coefficient (RH) in three, several micrometer long multigraphene samples of thickness between ~ 9 to ~ 30 nm in the temperature range 0.1 to 200 K and up to 0.2 T field. The temperature dependence of the longitudinal resistance of two of the samples indicates the contribution from embedded interfaces running parallel to the graphene layers. At low enough temperatures and fields RH is positive in all samples, showing a crossover to negative values at high enough fields and/or temperatures in samples with interfaces contribution. The overall results are compatible with the reported superconducting behavior of embedded interfaces in the graphite structure and indicate that the negative low magnetic field Hall coefficient is not intrinsic of the ideal graphite structure. [ABSTRACT FROM AUTHOR]

This letter presents theory and finite-difference time-domain calculations in excellent agreement with experiments for the transmission of a single subwavelength cylindrical hole in Ag metallic films. The authors discuss the very large enhancement in transmission by single holes in terms of surface plasmons at the interface of the hole. These are similar to the surface plasmons in metallic cylinders reported by Economou and co-workers [Phys. Rev. B 10, 3038 (1974); 24, 6908 (1981)]. The peak structures observed in experiments with arrays of holes are a consequence of interference of the beams transmitted by each hole and are determined by the hole periodicities. The role of the arrays in enhancement of the transmission due to surface plasmon polaritons appears to be marginal. [ABSTRACT FROM AUTHOR]

In this letter the authors show spin dependent transport experiments in nanoconstrictions ranging from 30 to 200 nm. These nanoconstrictions were fabricated by combined electron-beam lithography and thin film deposition techniques. Two types of geometries have been fabricated and investigated. They compare the experimental results with the theoretical estimation of the electrical resistance. Finally they show that the magnetoresistance for the different geometries does not scale with the resistance of the structure and obtain drops in voltage of 20 mV at 20 Oe. [ABSTRACT FROM AUTHOR]

We present experimental evidence of the capability of the scanning tunneling microscope (STM) to image the microstructure of surfaces with atomic resolution even at atmospheric pressure. Some examples of different types of materials (metal single crystals, graphite, semiconductor, oxide and metal films) are shown. We propose the STM as a highly sensitive standard for surface roughness determination of industrial finishing at atmospheric pressure. In our opinion, these results may open new perspectives in technology and industrial applications. [ABSTRACT FROM AUTHOR]

This letter revises the interpretation of recent experiments showing quantized conductance on GaAs/GaAlAs constrictions or point contacts in terms of coherent ballistic and sequential transport. Our calculations show by using a first iterative self-consistent procedure that the experimental data can also be reconciled with sequential transport. The mean free path concept in the constriction is discussed in comparison with that of the reservoirs. We conclude that, for the higher modes, the former is much smaller than the latter, implying that in the constriction the transport may be sequential. [ABSTRACT FROM AUTHOR]

We discuss the elastic coherent resistances of small contacts or constrictions between reservoirs. These resistances show an oscillatory behavior versus contact size, increase when the size of the contact decreases, and are dominant over the inelastic or residual resistances for realistic values of resistivities, temperature, and purity. [ABSTRACT FROM AUTHOR]

A new method to obtain information about local surface magnetic properties has been proposed recently. This new technique is based on the idea of measuring magnetic forces with a scanning tunneling force microscope. In this work we present a theoretical analysis of the relevant forces involved in magnetic force microscopy. Recent experiments with high-resolution images of laser-written domains in a magnetic thin film are discussed. [ABSTRACT FROM AUTHOR]

Controlled size clusters of Au with a diameter of 13 Å, prepared using a multiple expansion cluster source, have been supported on highly oriented pyrolytic graphite and observed with a scanning tunneling microscope. A reliable constant-current signature for a metallic cluster supported on a graphite substrate is identified. Images of the supported Au clusters are found to exhibit a narrow size distribution and a diameter which is in close agreement with the diameter predicted from conditions in the multiple expansion cluster source. [ABSTRACT FROM AUTHOR]

Presents an abstract of the study 'Theory of Magnetic Imaging by STM Force Microscopy,' conducted by J. J. Saenz and N. Garcia.

This letter shows that conducting ballistic and tunneling magnetoresistances have identical physical treatments and, therefore, it is not possible to distinguish whether an experiment is measuring, in oxide barriers, electron conduction through pinholes or tunneling because both types of conduction are governed by the same physics. Currents in both cases are calculated by matching wave functions at the electrodes (both are ballistic). Therefore, pinholes or small ballistic nanocontacts in the tunnel barrier allow conducting ballistic electrons that account for most of the current. We also show that, in the case of nonsuperconducting materials, e.g., magnetic materials, current-voltage characteristics are not suitable to distinguish one process from the other. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This letter shows that the ballistic magnetoresistance of Fe at room temperature and low magnetic fields is ten times smaller than for Ni and Co. The results are well explained by theory that provides a global understanding for 3d transition metals because, for Fe, the ratio of majority to minority spins at Fermi level is much smaller than for Ni and Co. The data indicate that conduction is carried out by majority d electrons in the case of Fe, in contrast to what happens for Ni and Co. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using the finite-difference time-domain method, we theoretically study elastic waves propagating in a two-dimensional composite consisting of aluminum cylinders embedded in mercury. The importance of the transverse components of the aluminum scatterers in the creation of the gaps is shown by switching off the transverse waves inside the aluminum. In that case, there are very narrow gaps or no gaps at all. In contrast, when the transverse components are on, as they should be, wide full band gaps appear for longitudinal incident waves. Since mercury supports only longitudinal waves, these are full elastic band gaps. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The reaction HOSO(2)+O(2)-->HO(2)+SO(3) (2) is of crucial importance for sulfuric acid formation in the atmosphere, and reliable thermochemical data are required for an adequate modeling. The currently least well known thermochemical quantity of reaction (2) is the enthalpy of formation of the hydroxysulfonyl radical (HOSO(2)). We report on high-level quantum chemical calculations to predict the binding energy of the HO-SO(2) bond and deduce a value for the enthalpy of formation of HOSO(2) using the most reliable thermodynamic data of OH and SO(2). On the basis of anharmonic vibrational frequencies from calculations at the fc-CCSD(T)/cc-pV(T+d)Z level of theory, the enthalpy of reaction at 0 K for the reaction OH+SO(2)-->HOSO(2) (1) was computed to be Delta(R)H(0 K)(1)=-109.4+/-2.0 kJ/mol and the thermal corrections result in Delta(R)H(298 K)(1)=-114.7+/-3.0 kJ/mol. From these values, we obtain Delta(f)H(0 K)(HOSO(2))=-366.6+/-2.5 and Delta(f)H(298 K)(HOSO(2))=-374.1+/-3.0 kJ/mol, respectively. Accordingly, Delta(R)H(0 K)(2)=-8.5+/-3.0 and Delta(R)H(298 K)(2)=-9.5+/-3.0 kJ/mol.