Multi-Sided Boundary Labeling

In the Boundary Labeling problem, we are given a set of $n$ points, referred to as sites, inside an axis-parallel rectangle $R$, and a set of $n$ pairwise disjoint rectangular labels that are attached to $R$ from the outside. The task is to connect the sites to the labels by non-intersecting rectilinear paths, so-called leaders, with at most one bend. In this paper, we study the Multi-Sided Boundary Labeling problem, with labels lying on at least two sides of the enclosing rectangle. We present a polynomial-time algorithm that computes a crossing-free leader layout if one exists. So far, such an algorithm has only been known for the cases in which labels lie on one side or on two opposite sides of $R$ (here a crossing-free solution always exists). The case where labels may lie on adjacent sides is more difficult. We present efficient algorithms for testing the existence of a crossing-free leader layout that labels all sites and also for maximizing the number of labeled sites in a crossing-free leader layout. For two-sided boundary labeling with adjacent sides, we further show how to minimize the total leader length in a crossing-free layout

Reliability of an adapted core strength endurance test battery in individuals with axial spondylarthritis

Objectives To adapt the core strength endurance test battery (aCSE), previously used for testing athletes, to a target group of patients with axial spondylarthritis (axSpA), to evaluate its intra-tester reliability and its associationswith disease-specific factors. Methods A cross-sectional study was conducted at axSpA exercise therapy groups, including both axSpA patients and the physiotherapist group leaders (PTs). The aCSE was used to measure the isometric strength endurance of the ventral, lateral, and dorsal core muscle chains (measured in seconds), as well as to assess the disease-specific factors of functional status, selfreported pain, and perceived strength performance. The aCSE was repeated after 7–14 days to measure intra-tester reliability for the same rater (PT group leader). Reliability was calculated as an intra-class correlation coefficient (ICC) using a nested design. The associations between ventral, lateral, and dorsal strength endurance and the disease-specific factors were calculated using Pearson correlation coefficients. Results Study participants were 13 PT group leaders and 62 axSpA patients. The latter were all capable of performing the aCSE, with the exception of one individual. A moderate to substantial intra-rater reliability (ICCs (95%CI)) was found for the ventral (0.54 (0.35, 0.74)), lateral (0.52 (0.33, 0.70)), and dorsal (0.71 (0.58, 0.86)) core muscle chains. None of the aCSE measures correlated with the disease-specific factors. Conclusion The aCSE was found to be a reliable test battery for assessing core strength endurance in axSpA patients. Interestingly, aCSE performance was not associated with any disease-specific factors

Enhanced field-emission investigation of aluminum

Enhanced field emission on high-purity aluminum has been investigated. The current/voltage characteristic (Fowler-Nordheim plot), the chemical composition as determined by Auger electron spectroscopy and X-ray microprobe analysis, and the topography of field-emitting sites were studied locally. In addition, results on the evolution of these sites under heat treatment, Ar/sup +/ sputtering, and exposure to atmosphere are presented. The field-emitting sites on aluminum are all related to particles approximately 30 mu m in size standing on the surface. The average emission over 1-cm/sup 2/ areas is little affected by the abovementioned surface treatments

Investigation of field emitting microstructures by scanning electron and scanning tunnelling microscopy

A study of enhanced field emission on broad area niobium cathodes is presented. Emitting sites have been investigated by field emission scans, scanning electron microscopy and scanning tunneling microscopy. All except one of 14 studied emitters are of micron or submicron size. A trend is observed for the emitting structures to be smaller than predicted from the protrusion model as is also demonstrated with the aid of a specific example of a field emitting site

A versatile low‐temperature scanning tunneling microscope

We present a new scanning tunneling microscope (STM) developed specifically for use at low temperatures within a standard helium cryostat. This compact STM (diameter 25 mm and length 61 mm) has been designed to be compatible with a superconducting magnet. It incorporates a novel approach system which operates in any orientation including the vertical one, without any mechanical connections to the STM. It is able to translate a sample by 30 Å steps in any orientation. The coarse and the fine approach are driven by a single piezoelectric tube via inertial slip‐stick motion of the sample holder. During the coarse approach, the translator can be moved over 15 mm at 0.25 mm/s against gravity. We have operated this STM down to 1.6 K and we have obtained images with atomic resolution on highly oriented pyrolitic graphite (HOPG) and NbSe2 from 300 K down to 90 K. This partially thermal compensated instrument is able to monitor temperature dependent surface changes on atomic scale in real time

Study of field‐emitting microstructures using a scanning tunneling microscope

Field emission from broad metal cathodes is known to be strongly enhanced at a small number of emitting sites per cm2 compared to the expected Fowler–Nordheim emission from ideal, flat surfaces. We have operated a scanning tunneling microscope (STM) in the field emission regime (typical tip voltage: +80 V) and measured the local field emission strengths and variations on niobium samples. With a modulation technique, which is an adaptation of the standard work function measurement, maps of the field enhancement factor β have been obtained. An example of an emission site is presented where STM topograph and β map are compared with a secondary electron microscope image and with field emission data obtained in a standard way using high‐voltage anodes. This demonstrates the capability of a scanning tunneling microscope to localize enhanced field emission sites (with typical β values of 50 in the present work) with high spatial resolution and to study surfaces down to the limit β=1

A vertical piezoelectric inertial slider

We have developed a linear translation device using piezoelectric‐induced slip‐stick motion. Reproducible single steps of about 30 Å, as well as continuous stepping with an overall translation speed of 0.25 mm/s, are routinely realized. The notable feature of this device is that this performance is achieved in the vertical orientation with the translator moving against gravity. This remarkable result is made possible using cycloidal functions instead of sawtooth signals to activate the motion. We have realized a very simple translator which can be used in any orientation with a displacement onset voltage of 15 V. The instrument was successfully tested in the temperature range from 1.6 to 300 K. Since no mechanical connections are required, this design is well suited for many applications, including scanning tunneling microscopy

Ballistic electron emission microscopy study of PtSi–<i>n</i>-Si(100) Schottky diodes

PtSi–n‐Si(100) Schottky contacts have been studied by ballistic electron emission microscopy (BEEM) for PtSi layers from 30 to 195 Å thickness. Locally measured barrier heights were typically close to or above those determined from the diode I–V characteristics, with a tendency to higher barriers for the thinner silicide films. The ballistic transmission probability also showed local variations with a clear tendency to decrease for increasing PtSi layer thicknesses, which can be understood in terms of the mean free path of hot electrons in PtSi. From simultaneous measurements at several voltages over the same area, maps of the apparent barrier height and transmission rate have been obtained showing sometimes strong local variations of these quantities. Very low and very high apparent barriers that were occasionally observed seemed to show that the simple BEEM picture is not always applicable, possibly due to interface roughness

Scanning tunneling spectroscopy of the Abrikosov flux lattice from the clean toward the dirty limit

Using a low-temperature scanning tunneling microscope, we have investigated the Abrikosov vortex lattice and its electronic structure on 2H-Nb₁₋ₓTaₓSe₂ single crystals for a range of Ta substitutions from x=0.00 to x=0.20 and with the magnetic field perpendicular to the basal plane. The material properties and in particular the electronic mean free path of 2H-Nb₁₋ₓTaₓSe₂ can be modified in a systematic manner by varying the Ta concentration. For all Ta substitutions considered, we show that the vortex lattice is aligned with the underlying atomic lattice. We find that the zero-bias conductance peak observed in the vortex core is strongly reduced both in intensity and spatial extent as x increases to 0.15, and vanishes when the Ta concentration reaches x=0.20. These results show for the first time the progressive destruction of the vortex core conductance peak with increasing disorder in a type-II superconductor

Scanning tunneling spectroscopy of a vortex core from the clean to the dirty limit

The local density of states of a superconducting vortex core has been measured as a function of disorder in the alloy system Nb1-xTaxSe2 using a low-temperature scanning tunneling microscope. The peak observed in the zero-bias conductance at a vortex center is found to be very sensitive to disorder. As the mean free path is decreased by substitutional alloying the peak gradually disappears and for x = 0.2 the density of states in the vortex center is found to be equal to that in the normal state. The vortex-core spectra hence may provide a sensitive measure of the quasiparticle scattering time