Mikkel Sørensen

Design of Single-Molecule Magnets: Insufficiency of the Anisotropy Barrier as the Sole Criterion

Determination of the electronic energy spectrum of a trigonal-symmetry mononuclear Yb(3+) single-molecule magnet (SMM) by high-resolution absorption and luminescence spectroscopies reveals that the first excited electronic doublet is placed nearly 500 cm(-1) above the ground one. Fitting of the paramagnetic relaxation times of this SMM to a thermally activated (Orbach) model {τ = τ0 × exp[ΔOrbach/(kBT)]} affords an activation barrier, ΔOrbach, of only 38 cm(-1). This result is incompatible with the spectroscopic observations. Thus, we unambiguously demonstrate, solely on the basis of experimental data, that Orbach relaxation cannot a priori be considered as the main mechanism determining the spin dynamics of SMMs. This study highlights the fact that the general synthetic approach of optimizing SMM behavior by maximization of the anisotropy barrier, intimately linked to the ligand field, as the sole parameter to be tuned, is insufficient because of the complete neglect of the interaction of the magnetic moment of the molecule with its environment. The Orbach mechanism is expected dominant only in the cases in which the energy of the excited ligand field state is below the Debye temperature, which is typically low for molecular crystals and, thus, prevents the use of the anisotropy barrier as a design criterion for the realization of high-temperature SMMs. Therefore, consideration of additional design criteria that address the presence of alternative relaxation processes beyond the traditional double-well picture is required.

[ReF6]2−: A Robust Module for the Design of Molecule‐Based Magnetic Materials

A facile synthesis of the [ReF6 ](2-) ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6 ](2-) unit in (PPh4 )2 [ReF6 ]⋅2 H2 O (1) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one-dimensional coordination polymer [Zn(viz)4 (ReF6 )]∞ (2, viz=1-vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy-plane-type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4 (ReF6 )]∞ (3) analogue in which the ferromagnetic Ni(II) -Re(IV) interaction (+10.8 cm(-1) ) dwarfs the coupling present in related cyanide-bridged systems. These results reveal [ReF6 ](2-) to be an unique new module for the design of molecule-based magnetic materials.

The first eastern migrations of people and knowledge into Scandinavia : evidence from studies of Mesolithic technology, 9th-8th millennium BC

In this paper a team of Scandinavian researchers identifies and describes a Mesolithic technological concept, referred to as ‘the conical core pressure blade’ concept, and investigates how this concept spread into Fennoscandia and across Scandinavia. Using lithic technological, contextual archaeological and radiocarbon analyses, it is demonstrated that this blade concept arrived with ‘post-Swiderian’ hunter-gatherer groups from the Russian plain into northern Fennoscandia and the eastern Baltic during the 9th millennium bc. From there it was spread by migrating people and/or as transmitted knowledge through culture contacts into interior central Sweden, Norway and down along the Norwegian coast. However it was also spread into southern Scandinavia, where it was formerly identified as the Maglemosian technogroup 3 (or the ‘Sværdborg phase’). In this paper it is argued that the identification and spread of the conical core pressure blade concept represents the first migration of people, technology and ideas into Scandinavia from the south-eastern Baltic region and the Russian plain.

The Prehistory of Inuit in Northeast Greenland

This article discusses recent archaeology fieldwork campaigns in Northeast Greenland, with a focus on investigating prehistoric Inuit remains. The paper endeavors to increase an understanding of the history of the prehistoric occupation of this High Arctic region, prehistoric groups’ responses to the distinct cooling throughout “the Little Ice Age” (sixteenth through nineteenth century), and their disappearance from the region. The article presents a critical review of earlier archaeological work and develops a relative chronology for the region. The fate of the Northeast Greenland Inuit is discussed with reference to subsistence and cultural constraints, concluding that a main reason for the discontinuity of human history in the region has to do with the geography that creates an isolating, island-like affect, factors causing severe demographic problems to the Inuit population through time.

Influence of acute and chronic streptozotocin-induced diabetes on the rat tendon extracellular matrix and mechanical properties

Diabetes is a major risk factor for tendinopathy, and tendon abnormalities are common in diabetic patients. The purpose of the present study was to evaluate the effect of streptozotocin (60 mg/kg)-induced diabetes and insulin therapy on tendon mechanical and cellular properties. Sprague-Dawley rats (n = 40) were divided into the following four groups: nondiabetic (control), 1 wk of diabetes (acute), 10 wk of diabetes (chronic), and 10 wk of diabetes with insulin treatment (insulin). After 10 wk, Achilles tendon and tail fascicle mechanical properties were similar between groups (P > 0.05). Cell density in the Achilles tendon was greater in the chronic group compared with the control and acute groups (control group: 7.8 ± 0.5 cells/100 μm(2), acute group: 8.3 ± 0.4 cells/100 μm(2), chronic group: 10.9 ± 0.9 cells/100 μm(2), and insulin group: 9.2 ± 0.8 cells/100 μm(2), P < 0.05). The density of proliferating cells in the Achilles tendon was greater in the chronic group compared with all other groups (control group: 0.025 ± 0.009 cells/100 μm(2), acute group: 0.019 ± 0.005 cells/100 μm(2), chronic group: 0.067 ± 0.015, and insulin group: 0.004 ± 0.004 cells/100 μm(2), P < 0.05). Patellar tendon collagen content was ∼32% greater in the chronic and acute groups compared with the control or insulin groups (control group: 681 ± 63 μg collagen/mg dry wt, acute group: 938 ± 21 μg collagen/mg dry wt, chronic: 951 ± 52 μg collagen/mg dry wt, and insulin group: 596 ± 84 μg collagen/mg dry wt, P < 0.05). In contrast, patellar tendon hydroxylysyl pyridinoline cross linking and collagen fibril organization were unchanged by diabetes or insulin (P > 0.05). Our findings suggest that 10 wk of streptozotocin-induced diabetes does not alter rat tendon mechanical properties even with an increase in collagen content. Future studies could attempt to further address the mechanisms contributing to the increase in tendon problems noted in diabetic patients, especially since our data suggest that hyperglycemia per se does not alter tendon mechanical properties.

At the edge. High Arctic Walrus hunters during the Little Ice Age

A multi-disciplinary study of settlement in north-east Greenland found that life in this High Arctic zone was actually favoured by the climate brought in by the Little Ice Age (fifteenth–nineteenth century). Extensive ice cover meant high mobility, and the rare polynyas — small patches of permanently open coastal water — provided destinations, like oases, where huge numbers of migrating marine mammals and birds congregated. One such place was Walrus Island on Sirius Water, a veritable processing plant for walrus, where every spring Thule people stocked up meat supplies that would get the rest of the region through the winter. It was a further drop in the temperature in the mid nineteenth century that led to the region being abandoned.

The Arrival and Development of Pressure Blade Technology in Southern Scandinavia

The first pressure blade concept in southern Scandinavia is identified within the Maglemosian techno-complex 3, dated to the Boreal-Atlantic transition, in the 8th millennium B.C. From technological analysis of blade products in adjacent regions, it is found that a similar concept existed through the eastern Baltic lowland and into the Western Russian plain, where it is described in the post-Swiderian cultures and dated to the 9th millennium B.C. Due to the technological nature of pressure blade technology, a general continuity in the Maglemosian tradition and a clear indication of a similar pressure blade concept in the eastern Baltic region prior to its appearance in southern Scandinavia, it is argued that the first pressure blade concept of southern Scandinavia primarily arrived from the East as “borrowed” knowledge.

Chemical tunnel-splitting-engineering in a dysprosium-based molecular nanomagnet

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin–orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C4) to pseudo-linear (D4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting.Suppression of quantum tunneling in molecular magnets is key for their magnetic behaviours to be exploitable. Here, the authors show that tuning the geometry of lanthanide single-ion magnets leads to a suppression of the quantum tunneling, finding a three-fold reduction of the tunnel splitting upon changing the crystal field symmetry.

Impact of TGF-β inhibition during acute exercise on achilles tendon extracellular matrix

The purpose of this study was to evaluate the role of TGF-β1 in regulating tendon extracellular matrix after acute exercise. Wistar rats exercised (n = 15) on a treadmill for four consecutive days (60 min/day) or maintained normal cage activity. After each exercise bout, the peritendinous space of each Achilles tendon was injected with a TGF-β1 receptor inhibitor or sham. Independent of group, tendons injected with inhibitor exhibited ~50% lower Smad 3 (Ser423/425) (P < 0.05) and 2.5-fold greater ERK1/2 phosphorylation (P < 0.05) when compared with sham (P < 0.05). Injection of the inhibitor did not alter collagen content in either group (P > 0.05). In exercised rats, hydroxylyslpyridinoline content and collagen III expression were lower (P < 0.05) in tendons injected with inhibitor when compared with sham. In nonexercised rats, collagen I and lysyl oxidase (LOX) expression was lower (P < 0.05) in tendons injected with inhibitor when compared with sham. Decorin expression was not altered by inhibitor in either group (P > 0.05). On the basis of evaluation of hematoxylin and eosin (H&E) stained cross sections, cell numbers were not altered by inhibitor treatment in either group (P > 0.05). Evaluation of H&E-stained sections revealed no effect of inhibitor on collagen fibril morphology. In contrast, scores for regional variation in cellularity decreased in exercised rats (P < 0.05). No differences in fiber arrangement, structure, and nuclei form were noted in either group (P > 0.05). Our findings suggest that TGF-β1 signaling is necessary for the regulation of tendon cross-link formation, as well as collagen and LOX gene transcription in an exercise-dependent manner.

Eastern Arctic Under Pressure: From Paleoeskimo to Inuit Culture (Canada and Greenland)

Pressure microblade production (Fig. 15.1) appeared with the arrival of the Paleoeskimo people (4500–800 B.P.) in the Eastern Arctic, long after the technique was established in other areas of the world. Previous assumptions have all too quickly proposed that the Paleoeskimo produced microblades by ‘pressing them off’ from the core. As a result, there was no real attempt made to analyse the techniques employed to detach microblades in later studies. In addition, early studies did not focus on lithic technology in any great detail, which likely explains why our present knowledge is limited with regard to detachment techniques in the Arctic. This study seeks to improve upon our current knowledge of the detachment technique for microblade production employed by the Paleoeskimo.