Theory of a magnetic microscope with nanometer resolution

We propose a theory for a type of apertureless scanning near field microscopy that is intended to allow the measurement of magnetism on a nanometer length scale. A scanning probe, for example a scanning tunneling microscope (STM) tip, is used to scan a magnetic substrate while a laser is focused on it. The electric field between the tip and substrate is enhanced in such a way that the circular polarization due to the Kerr effect, which is normally of order 0.1% is increased by up to two orders of magnitude for the case of a Ag or W tip and an Fe sample. Apart from this there is a large background of circular polarization which is non-magnetic in origin. This circular polarization is produced by light scattered from the STM tip and substrate. A detailed retarded calculation for this light-in-light-out experiment is presented.Comment: 17 pages, 8 figure

Equilibrium shapes and energies of coherent strained InP islands

The equilibrium shapes and energies of coherent strained InP islands grown on GaP have been investigated with a hybrid approach that has been previously applied to InAs islands on GaAs. This combines calculations of the surface energies by density functional theory and the bulk deformation energies by continuum elasticity theory. The calculated equilibrium shapes for different chemical environments exhibit the {101}, {111}, {\=1\=1\=1} facets and a (001) top surface. They compare quite well with recent atomic-force microscopy data. Thus in the InP/GaInP-system a considerable equilibration of the individual islands with respect to their shapes can be achieved. We discuss the implications of our results for the Ostwald ripening of the coherent InP islands. In addition we compare strain fields in uncapped and capped islands.Comment: 10 pages including 6 figures. Submitted to Phys. Rev. B. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Temporal Trends in Vertebral Size and Shape from Medieval to Modern-Day

Human lumbar vertebrae support the weight of the upper body. Loads lifted and carried by the upper extremities cause significant loading stress to the vertebral bodies. It is well established that trauma-induced vertebral fractures are common especially among elderly people. The aim of this study was to investigate the morphological factors that could have affected the prevalence of trauma-related vertebral fractures from medieval times to the present day. To determine if morphological differences existed in the size and shape of the vertebral body between medieval times and the present day, the vertebral body size and shape was measured from the 4th lumbar vertebra using magnetic resonance imaging (MRI) and standard osteometric calipers. The modern samples consisted of modern Finns and the medieval samples were from archaeological collections in Sweden and Britain. The results show that the shape and size of the 4th lumbar vertebra has changed significantly from medieval times in a way that markedly affects the biomechanical characteristics of the lumbar vertebral column. These changes may have influenced the incidence of trauma- induced spinal fractures in modern populations

A volumetric technique for fossil body mass estimation applied to Australopithecus afarensis

Fossil body mass estimation is a well established practice within the field of physical anthropology. Previous studies have relied upon traditional allometric approaches, in which the relationship between one/several skeletal dimensions and body mass in a range of modern taxa is used in a predictive capacity. The lack of relatively complete skeletons has thus far limited the potential application of alternative mass estimation techniques, such as volumetric reconstruction, to fossil hominins. Yet across vertebrate paleontology more broadly, novel volumetric approaches are resulting in predicted values for fossil body mass very different to those estimated by traditional allometry. Here we present a new digital reconstruction of Australopithecus afarensis (A.L. 288-1; ‘Lucy’) and a convex hull-based volumetric estimate of body mass. The technique relies upon identifying a predictable relationship between the ‘shrink-wrapped’ volume of the skeleton and known body mass in a range of modern taxa, and subsequent application to an articulated model of the fossil taxa of interest. Our calibration dataset comprises whole body computed tomography (CT) scans of 15 species of modern primate. The resulting predictive model is characterized by a high correlation coefficient (r2 = 0.988) and a percentage standard error of 20%, and performs well when applied to modern individuals of known body mass. Application of the convex hull technique to A. afarensis results in a relatively low body mass estimate of 20.4 kg (95% prediction interval 13.5–30.9 kg). A sensitivity analysis on the articulation of the chest region highlights the sensitivity of our approach to the reconstruction of the trunk, and the incomplete nature of the preserved ribcage may explain the low values for predicted body mass here. We suggest that the heaviest of previous estimates would require the thorax to be expanded to an unlikely extent, yet this can only be properly tested when more complete fossils are available

Jännevirran sillan väsymismitoitus mitatulla liikennekuormalla

Työssä verrataan Eurokoodin mukaisia väsytyskuormakaavioita Suomessa mitattuihin todellisiin liikennekuormiin. Eurokoodin mukainen väsymismitoitus tehdään väsytyskuormakaavioille FLM 3 ja FLM 4. Mitatut liikennekuormat on saatu Suomessa tehdyistä liikenteen automaattisista mittauksista, akselimassatutkimuksesta ja silta-WIM -mittauksista. Väsymismitoitus tehdään Jännevirran sillalle. Silta on teräksinen jatkuva betonikantinen liittopalkkisilta, jonka jännemitat ovat 50 + 70 + 100 + 120 + 100 + 70 + 50 m ja hyödyllinen leveys on 15,25 m. Tutkittavat detaljityypit ovat: laipan jatkaminen, lisälevyn päättäminen, vaarnan hitsi laippaan ja pystyjäykisteen hitsi alalaippaan. Tavoitteena on selvittää, miten tarkasti eri liikennekuormilla tehdyt mitoitukset vastaavat toisiaan ja onko FLM 3 mahdollisesti yli- tai alimitoittava todelliseen liikennekuormaan verrattuna tutkittavassa pitkiä jännevälejä sisältävässä sillassa. Mitatusta liikennekuormasta arvioidaan myös ajoneuvojen painorajoitusten noston vaikutusta liikenteen väsytyskuormittavuuteen. Lisäksi työssä perehdytään hitsin jälkikäsittelymenetelmiin, joilla voi parantaa detaljien väsymiskestävyyttä. Laskennan tuloksissa sillan kahdessa lyhyimmässä aukossa (L = 50 m ja 70 m) sijaitsevien detaljien väsymismitoituksessa FLM 3 on ylimitoittava. Kahden pisimmän aukon (L =100 m ja 120 m) kriittisissä detaljeissa FLM 3 on alimitoittava. Detaljien väsymisvauriot pysyvät kuitenkin sallituissa rajoissa. Jänneväliltään pitkissä aukoissa mitattujen liikennekuormien aiheuttama väsymisvaurio on suuri, koska pitkälle jännevälille mahtuu kulkemaan monta raskasta ajoneuvoa peräkkäin. FLM 4 mitoituksen tulokset ovat epäluotettavia muihin väsytyskuormiin verrattuna. Tutkimuksen tulosten perusteella FLM 3 mitoitus vaatii kehittämistä, jotta se soveltuu käytettäväksi Suomessa jänneväliltään pitkille silloille. Myös FLM 4 mitoitus pitäisi kehittää Suomen ajoneuvoliikennettä vastaavaksi.In this work Eurocode Fatigue Load Models are compared with real traffic loads measured in Finland. The fatigue design conforming to Eurocode is done with FLM 3 and FLM 4. The measured traffic loads have been obtained from automatic traffic measurements, axle load survey and bridge weigh in motion measurements that have been carried out in Finland. The fatigue design is done to the Jännevirta Bridge. The bridge is a continuous composite girder bridge, which spans are 50 + 70 + 100 + 120 + 100 + 70 + 50 m and the effective width is 15.25 m. The details chosen for the research are: the splice of the flange, the additional plate closure, the shear stud welded to the flange and the vertical stiffener welded to the lower flange. The aim is to find out how closely the fatigue design done by different traffic loads correspond to each other and whether the FLM 3 is over- or underestimating fatigue damage compared with the actual traffic load in the bridge with long spans. The change in fatigue damage due to increased vehicle weight limits is examined based on measured traffic loads. In addition, the post weld treatment methods that can improve the fatigue strength of the details are studied in the work. The calculation results show that the FLM 3 is overestimating fatigue damage in the details located at the two shortest opening of the bridge (L = 50 m and 70 m). In critical details located at the two longest opening of the bridge (L = 100 m and 120 m) the FLM 3 is underestimating fatigue damage. However, the fatigue damage of all details remains within the permitted limits. The fatigue damage is high in the long spans because many heavy vehicles in a row fit onto the long span. The FLM 4 results are unreliable in comparison with other fatigue loading. Based on the results FLM 3 requires the development so that it is suitable for use in Finland for long span bridges. Also FLM 4 should be developed to match the Finnish vehicle traffic