Lorentz TEM investigation of the switching behavior in artificial spin ice building blocks

Frustration – the inability to simultaneously satisfy all interactions – occurs in a wide range of systems including neural networks, water ice and magnetic systems. An example of the latter is the so called spin-ice in pyrochlore materials [1] which have attracted a lot of interest not least due to the emergence of magnetic monopole defects when the ‘ice rules’ governing the local ordering breaks down [2]. However it is not possible to directly measure the frustrated property – the direction of the magnetic moments – in such spin ice systems with current experimental techniques. This problem can be solved by instead studying artificial spin-ice systems where the molecular magnetic moments are replaced by nanoscale ferromagnetic islands [3-8]. Two different arrangements of the ferromagnetic islands have been shown to exhibit spin ice behaviour: a square lattice maintaining four moments at each vertex [3,8] and the Kagome lattice which has only three moments per vertex but equivalent interactions between them [4-7]. Magnetic monopole defects have been observed in both types of lattices [7-8]. One of the challenges when studying these artificial spin-ice systems is that it is difficult to arrive at the fully demagnetised ground-state [6-8].
Here we present a study of the switching behaviour of building blocks of the Kagome lattice influenced by the termination of the lattice. Ferromagnetic islands of nominal size 1000 nm by 100 nm were fabricated in five island blocks using electron-beam lithography and lift-off techniques of evaporated 18 nm Permalloy (Ni80Fe20) films. Each block consists of a central island with four arms terminated by a different number and placement of ‘injection pads’, see Figure 1. The islands are single domain and magnetised along their long axis. The structures were grown on a 50 nm thick electron transparent silicon nitride membrane to allow TEM observation, which was back-coated with a 5 nm film of Au to prevent charge build-up during the TEM experiments.
To study the switching behaviour the sample was subjected to a magnetic field strong enough to magnetise all the blocks in one direction, see Figure 1. Each block obeys the Kagome lattice ‘ice-rules’ of “2-in, 1-out” or “1-in, 2-out” in this fully magnetised state. Fresnel mode Lorentz TEM images of the sample were then recorded as a magnetic field of increasing magnitude was applied in the opposite direction. While the Fresnel mode is normally used to image magnetic domain structures [9] for these types of samples it is possible to deduce the direction of the magnetisation from the Lorentz contrast [5]. All images were recorded at the same over-focus judged to give good Lorentz contrast.
The magnetisation was found to switch at different magnitudes of the applied field for nominally identical blocks. However, trends could still be identified: all the blocks with any injection pads, regardless of placement and number, switched the direction of the magnetisation of their central island at significantly smaller magnitudes of the applied magnetic field than the blocks without injection pads. It can therefore be concluded that the addition of an injection pad lowers the energy barrier to switching the connected island, acting as a nucleation site for monopole defects. In these five island blocks the defects immediately propagate through to the other side, but in a larger lattice the monopoles could potentially become trapped at a vertex and observed [10].
References

[1] M J Harris et al, Phys Rev Lett 79 (1997) p.2554.
[2] C Castelnovo, R Moessner and S L Sondhi, Nature 451 (2008) p. 42.
[3] R F Wang et al, Nature 439 (2006) 303.
[4] M Tanaka et al, Phys Rev B 73 (2006) 052411.
[5] Y Qi, T Brintlinger and J Cumings, Phys Rev B 77 (2008) 094418.
[6] E Mengotti et al, Phys Rev B 78 (2008) 144402.
[7] S Ladak et al, Nature Phys 6 (2010) 359.
[8] C Phatak et al, Phys Rev B 83 (2011) 174431.
[9] J N Chapman, J Phys D 17 (1984) 623.
[10] The authors gratefully acknowledge funding from the EPSRC under grant number EP/D063329/1.

Effectiveness of granular columns in containing settlement

Laboratory-based research studies and full-scale evaluations of the behaviour of ground improved with granular columns are ample regarding bearing capacity, but limited in respect to the settlement response. This paper presents a laboratory model study that considers the settlement performance of isolated pad footings bearing on reinforced sand deposits under the influence of a fluctuating groundwater table. This is a particularly onerous condition for loose sand deposits in coastal areas which may undergo significant collapse settlement over time. Loose and dense experimental sand beds were constructed and the performance of rigid footings under a maintained load and bearing on sand incorporating different column configurations were monitored under cycling of the water table over a period of 28 days, with one filling/empting cycle every 18 h. It was found that settlement, while greatly reduced compared with unreinforced footings, was ongoing and typically occurred at a much greater rate for loose sand than dense sand. Also, settlement rates were slightly higher for fully penetrating than partially penetrating columns and also for footings reinforced by a column group rather than a single column. This was attributed to the migration of sand grains into the larger column voids.

Infrastructure and the Architectures of Modernity in Ireland 1916-2016

At the formation of the new Republic of Ireland, the construction of new infrastructures was seen as an essential element in the building of the new nation, just as the adoption of international style modernism in architecture was perceived as a way to escape the colonial past. Accordingly, infrastructure became the physical manifestation, the concrete identity of these objectives and architecture formed an integral part of this narrative. Moving between scales and from artefact to context, Infrastructure and the Architectures of Modernity in Ireland 1916-2016 provides critical insights and narratives on what is a complex and hitherto overlooked landscape, one which is often as much international as it is Irish. In doing so, it explores the interaction between the universalising and globalising tendencies of modernisation on one hand and the textures of local architectures on the other.

The book shows how the nature of technology and infrastructure is inherently cosmopolitan. Beginning with the building of the heroic Shannon hydro-electric facility at Ardnacrusha by the German firm of Siemens-Schuckert in the first decade of independence, Ireland became a point of varying types of intersection between imported international expertise and local need. Meanwhile, at the other end of the century, by the year 2000, Ireland had become one of the most globalized countries in the world, site of the European headquarters of multinationals such as Google and Microsoft. Climatically and economically expedient to the storing and harvesting of data, Ireland has subsequently become a repository of digital information farmed in large, single-storey sheds absorbed into anonymous suburbs. In 2013, it became the preferred site for Intel to design and develop its new microprocessor chip: the Galileo. The story of the decades in between, of shifts made manifest in architecture and infrastructure from the policies of economic protectionism, to the opening up of the country to direct foreign investment and the embracing of the EU, is one of the influx of technologies and cultural references into a small country on the edges of Europe as Ireland became both a launch-pad and testing ground for a series of aspects of designed modernity.

Cadaveric fascia lata pubovaginal slings:early results on safety, efficacy and patient satisfaction

Objective To prospectively evaluate and quantify the efficacy of cadaveric fascia lata (CFL) as an allograft material in pubovaginal sling placement to treat stress urinary incontinence (SUI).

Patients and methods Thirty-one women with SUI (25 type II and six type III; mean age 63 years, range 40-75) had a CFL pubovaginal sling placed transvaginally. The operative time, blood loss, surgical complications and mean hospital stay were all documented. Before and at 4 months and 1 year after surgery each patient completed a 3-day voiding diary and validated voiding questionnaires (functional inquiry into voiding habits, Urogenital Distress Inventory and Incontinence Impact Questionnaire, including visual analogue scales).

Results The mean (range) operative time was 71 (50-120) min, blood loss 78.7 (20-250) mL and hospital stay 1.2 (1-2) days; there were no surgical complications. Over the mean follow-up of 13.5 months, complete resolution of SUI was reported by 29 (93%) patients. Overactive bladder symptoms were present in 23 (74%) patients before surgery, 21 (68%) at 4 months and two (6%) at 1 year; 80% of patients with low (<15 cmH (2) O) voiding pressures before surgery required self-catheterization afterward, as did 36% at 4 months, but only one (3%) at 1 year. Twenty-four (77%) patients needed to adopt specific postures to facilitate voiding. After surgery there was a significant reduction in daytime frequency, leakage episodes and pad use (P <0.05). The severity of leak and storage symptoms was also significantly less (P <0.002), whilst the severity of obstructive symptoms remained unchanged. Mean subjective levels of improvement were 69% at 4 months and 85% at 1 year, with corresponding objective satisfaction levels of 61% and 69%, respectively. At 1 year, approximate to 80% of the patients said they would undergo the procedure again and/or recommend it to a friend.

Conclusion Placing a pubovaginal sling of CFL allograft is a highly effective, safe surgical approach for resolving SUI, with a short operative time and rapid recovery. Storage symptoms are significantly improved, and subjective improvement and satisfaction rates are high.

Infra-Éireann: Making Ireland Modern - Irish Pavilion for the 14th Architectural biennale, Venice 2014.

After an open competition, we were selected to commission, curate and design the Irish pavilion for the Venice biennale 2014. Our proposal engage with the role of infrastructure and architecture in the cultural development of the new Irish state 1914-2014. This curatorial programme was realised in a demountable, open matrix pavilion measuring 12 x 5 x 6 metres.

How modernity is absorbed into national cultures usually presupposes an attachment to previous conditions and a desire to reconcile the two. In an Irish context, due to the processes of de-colonisation and political independence, this relationship is more complicated.

In 1914, Ireland was largely agricultural and lacked any significant industrial complex. The construction of new infrastructures after independence in 1921 became central to the cultural imagining of the new nation. The adoption of modernist architecture was perceived as a way to escape the colonial past. As the desire to reconcile cultural and technological aims developed, these infrastructures became both the physical manifestation and concrete identity of the new nation with architecture an essential element in this construct.

Technology and infrastructure are inherently cosmopolitan. Beginning with the Shannon hydro-electric facility at Ardnacrusha (1929) involving the German firm of Siemens-Schuckert, Ireland became a point of various intersections between imported international expertise and local need. By the turn of the last century, it had become one of the most globalised countries in the world, site of the European headquarters of multinationals such as Google and Microsoft. Climatically and economically expedient to the storing and harvesting of data, Ireland has subsequently become an important repository of digital information farmed in large, single-storey sheds absorbed into dispersed suburbs. In 2013, it became the preferred site for Intel to design and develop its new microprocessor board, the Galileo, a building block for the internet of things.

The story of the decades in between, of shifts made manifest in architecture and infrastructure, from the policies of economic protectionism to the embracing of the EU is one of the influx of technologies and cultural references into a small country on the edges of Europe: Ireland as both a launch-pad and testing ground for a series of aspects of designed modernity.

Padrões de crescimento em otólitos de larvas de Pomatoschistus pictus (Pisces, Gobiidae)

Dissertação mest., Biologia Marinha, Universidade do Algarve, 2006

Padrões de distribuição e taxonomia para os porifera da região central do Algarve

Dissertação de mest., Biologia Marinha, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2007

Padrões temporais de fornecimento de Megalopas de Carcinus Maenas na Ria de Aveiro: influência dos ventos e das marés

Dissertação mest., Biologia marinha - Ecologia e conservação marinha, Universidade do Algarve, 2007

Padrões de distribuição da abundância larvar de crustáceos decápodes na baía de Cascais

Dissertação mest., Biologia marinha, Universidade do Algarve, 2009

Padrões temporais e verticais de pequena escala na ocorrência de larvas de peixe na Ria de Aveiro, Portugal

Dissertação de mest., Biologia Marinha (Ecologia e Conservação Marinha), Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2010

Padrões verticais e inter-anuais nas assembleias de larvas de peixe junto ao substrato rochoso do Parque Marinho da Arrábida

Dissertação de mest., Biologia Marinha, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2009

Improved extraction of arabinoxylans from rye bran and production of health beneficial oligosaccharides

Dissertação de mest., Engenharia Biológica, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011

Generate disaggregated soil allocation data using a Minimum Cross Entropy Model

Montado ecosystem in the Alentejo Region, south of Portugal, has enormous agro-ecological and economics heterogeneities. A definition of homogeneous sub-units among this heterogeneous ecosystem was made, but for them is disposal only partial statistical information about soil allocation agro-forestry activities. The paper proposal is to recover the unknown soil allocation at each homogeneous sub-unit, disaggregating a complete data set for the Montado ecosystem area using incomplete information at sub-units level. The methodological framework is based on a Generalized Maximum Entropy approach, which is developed in thee steps concerning the specification of a r order Markov process, the estimates of aggregate transition probabilities and the disaggregation data to recover the unknown soil allocation at each homogeneous sub-units. The results quality is evaluated using the predicted absolute deviation (PAD) and the "Disagegation Information Gain" (DIG) and shows very acceptable estimation errors.

Protein deiminases: new players in the developmentally regulated loss of neural regenerative ability

Spinal cord regenerative ability is lost with development, but the mechanisms underlying this loss are still poorly understood. In chick embryos, effective regeneration does not occur after E13, when spinal cord injury induces extensive apoptotic response and tissue damage. As initial experiments showed that treatment with a calcium chelator after spinal cord injury reduced apoptosis and cavitation, we hypothesized that developmentally regulated mediators of calcium-dependent processes in secondary injury response may contribute to loss of regenerative ability. To this purpose we screened for such changes in chick spinal cords at stages of development permissive (E11) and non-permissive (E15) for regeneration. Among the developmentally regulated calcium-dependent proteins identified was PAD3, a member of the peptidylarginine deiminase (PAD) enzyme family that converts protein arginine residues to citrulline, a process known as deimination or citrullination. This post-translational modification has not been previously associated with response to injury. Following injury, PAD3 up-regulation was greater in spinal cords injured at E15 than at E11. Consistent with these differences in gene expression, deimination was more extensive at the non-regenerating stage, E15, both in the gray and white matter. As deimination paralleled the extent of apoptosis, we investigated the effect of blocking PAD activity on cell death and deiminated-histone 3, one of the PAD targets we identified by mass-spectrometry analysis of spinal cord deiminated proteins. Treatment with the PAD inhibitor, Cl-amidine, reduced the abundance of deiminated-histone 3, consistent with inhibition of PAD activity, and significantly reduced apoptosis and tissue loss following injury at E15. Altogether, our findings identify PADs and deimination as developmentally regulated modulators of secondary injury response, and suggest that PADs might be valuable therapeutic targets for spinal cord injury.