Co2MnSi Heusler alloy thin films

This thesis investigates the growth of intermetallic compounds by co-sputtering from single elemental targets. The preliminary work involved constructing a sputtering set-up to grow a binary alloy (Sm-Co) and investigating how to control the composition spread that was obtained. Having achieved this, a larger sputtering flange was built up to grow the ternary Heusler alloy, Co2MnSi. Co2MnSi has been predicted to be a half-metallic ferromagnet, which means that there is an energy gap in the minority spin band at the Fermi energy. This leads to 100 % spin polarised conduction electrons, which would enable ideal spin-device performance to be obtained. Co2MnSi is particularly promising because it is predicted to have a large energy gap in the minority band of ~0.4 eV and has the highest Curie temperature among the known Heuslers of 985 K. Initially, Co2MnSi was grown on a-plane sapphire and stoichiometric films were single phase and highly (110) textured, without the use of a seed layer. They exhibited the bulk value of the saturation magnetisation, Ms and films grown at the highest deposition temperature (715 K) showed the lowest resistivity (47 µΩcm at 4.2 K) and the lowest room temperature coercivity (18 Oe). The spin polarisation of the transport current, Pt of a 400 nm film grown at this deposition temperature was 54 %, consistent with measurements on bulk single crystals. Ms decreased with decreasing film thickness indicating a graded disorder. By growing on GaAs (001), which has a similar lattice parameter to Co2MnSi it was expected that this disordered region would be confined to the first few atomic layers. However, this was not the case because interfacial reactions resulted in the formation of an epitaxial Mn-As region, and a thin interfacial layer that was Co-Ga rich. This prevented the lattice matching of the Co2MnSi to the GaAs(001) hence hindering epitaxial growth of the Heusler. The reaction zone also meant that films exhibited a Ms slightly below the bulk value. The expected fourfold anisotropy was not obtained for this cubic material, which is most likely due to the anisotropy of the reconstructed GaAs surface. In spite of this anomalous behaviour, Pt was 55 %, similar to the result obtained on sapphire, indicating that either Pt is independent of orientation or that the Heusler surface reconstructs in the same way. Films showed some improved properties to films grown on a-plane sapphire, indicating the potential of growing on this technologically important substrate. With this in mind, pseudo spin valves involving Co2MnSi as one of the ferromagnetic electrodes were fabricated in both the CIP and CPP configurations. Clear low-field spin-valve contributions were observed at 15 K but the MR values are much lower than that expected from a PSV with a predicted 100 % spin polarised electrode.EPSR

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Label free biosensor for screening estrogenic activity

640-645Estrogens and estrogen mimics prevalent in aquatic environment are of great environmental concern because of their endocrine disrupting and carcinogenic activities. Looking to the wide variety of natural as well as structurally different synthetic estrogen mimics, a reliable in-vitro assay is required for screening the estrogenic activity of endocrine disrupting compounds (EDCs). Surface plasmon resonance (SPR) is one of the most promising analytical tools to monitor the high-performance biomolecular interactions in a label free, real time format. Present paper demonstrates a facile SPR based affinity bioassay employing estrogen receptor-α, human (hERα) functionalized self assembled monolayer covalently bound onto the gold sensor chip as recognition species. A successful interaction of potential estrogen mimics with estrogen receptor is evidenced by net rise in SPR angle. The assay has been validated in terms of optimum experimental conditions and specificity with estrogen as a positive control showing maximum estrogenic activity. As a proof of concept, proposed affinity assay is tested for screening the estrogenic activity of progesterone, pregnenolone, tamoxifen, and bisphenol-A as representative examples of potential EDCs of different classes

Mukhanov-Sasaki equation in manifestly gauge-invariant linearized cosmological perturbation theory with dust reference fields

The aim of this article is to understand the role of dust reference fields, often also called clocks, on cosmological perturbations around a flat FLRW universe. We derive the Mukhanov-Sasaki (MS) equation for the Brown-Kuchar (BK) and Gaussian dust models, which both consider four dust fields as reference fields. The reduced phase space of Dirac observables, that is the gauge-invariant part of the theory, is constructed by means of an observable map applied to all elementary phase space variables of the coupled system, consisting of gravity, a massive scalar field and the dust degrees of freedom. The evolution of these observables is governed by a so called physical Hamiltonian which can be derived once the set of reference fields are chosen and differs for each model. First, the reduced phase space as well as the corresponding equations of motion are derived for full general relativity. Then from this, the gauge-invariant version of the equations of motion for the background are derived which contain a fingerprint of the dust reference fields. Afterwards we study linear cosmological perturbations around a FLRW metric using the scalar-vector-tensor decomposition and derive the equation of motion for the MS variable in this formalism for a chosen set of variables on the reduced phase space and expressed in terms of Dirac observables. The MS equation involves additional contributions that can be understood as back reactions from the dust reference fields. These additional dust contributions to the MS equation were absent if the dust energy and momentum density as well as their perturbations are vanishing. The nature of the correction terms suggest that BK and Gaussian dust reference fields contribute differently. Using numerical simulations we study the behavior of the dust contributions to the MS equation during inflation.Comment: Revised version. Analysis and comparison of two dust models extended to investigate Mukhanov-Sasaki variable with now corrected contribution for Brown-Kuchar model. Figures added and updated. To appear in Phys. Rev.

Deficiency of Ataxia Telangiectasia Mutated Kinase Delays Inflammatory Response in the Heart Following Myocardial Infarction

Background: Ataxia-telangiectasia results from mutations in ataxia telangiectasia mutated kinase (ATM) gene. We recently reported that ATM deficiency attenuates left ventricular (LV) dysfunction and dilatation 7 days after myocardial infarction (MI) with increased apoptosis and fibrosis. Here we investigated the role of ATM in the induction of inflammatory response, and activation of survival signaling molecules in the heart acute post-MI. Methods and Results: LV structure, function, inflammatory response, and biochemical parameters were measured in wild-type (WT) and ATM heterozygous knockout (hKO) mice 1 and 3 days post-MI. ATM deficiency had no effect on infarct size. MI-induced decline in heart function, as measured by changes in percent fractional shortening, ejection fraction and LV end systolic and diastolic volumes, was lower in hKO-MI versus WT-MI (n=10 to 12). The number of neutrophils and macrophages was significantly lower in the infarct LV region of hKO versus WT 1 day post-MI. Fibrosis and expression of a-smooth muscle actin (myofibroblast marker) were higher in hKO-MI, while active TGF-β1 levels were higher in the WT-MI 3 days post-MI. Myocyte cross-sectional area was higher in hKO-sham with no difference between the two MI groups. MMP-9 protein levels were similarly increased in the infarct LV region of both MI groups. Apoptosis was significantly higher in the infarct LV region of hKO at both time points. Akt activation was lower, while Bax expression was higher in hKO-MI infarct. Conclusion: ATM deficiency results in decreased dilative remodeling and delays inflammatory response acute post-MI. However, it associates with increased fibrosis and apoptosis

Classifying Spending Behavior using Socio-Mobile Data

Human spending behavior is essentially social. This work motivates and grounds the use of mobile phone based social interaction features for classifying spending behavior. Using a data set involving 52 adults (26 couples) living in a community for over a year, we find that social behavior measured via face-to-face interaction, call, and SMS logs, can be used to predict the spending behavior for couples in terms of their propensity to explore diverse businesses, become loyal customers, and overspend. Our results show that mobile phone based social interaction patterns can provide more predictive power on spending behavior than personality based features. Interestingly, we find that more social couples also tend to overspend. Obtaining such insights about couple level spending behavior via novel social-computing frameworks can be of vital importance to economists, marketing professionals, and policy makers.European Commission (PERSI project inside the Marie Curie Cofund 7th framework

Enhanced sensitivity to optimistic cues is manifested in brain structure: A voxel-based morphometry study

Recent research shows that congruent outcomes are more rapidly (and incongruent less rapidly) detected when individuals receive optimistic rather than pessimistic cues, an effect that was termed optimism robustness. In the current voxel-based morphometry study, we examined whether optimism robustness has a counterpart in brain structure. The participants’ task was to detect two different letters (symbolizing monetary gain or loss) in a visual search matrix. Prior to each onset of the search matrix, two different verbal cues informed our participants about a high probability to gain (optimistic expectancy) or lose (pessimistic expectancy) money. The target presented was either congruent or incongruent with these induced expectancies. Optimism robustness revealed in the participants’ reaction times correlated positively with gray matter volume (GMV) in brain regions involved in selective attention (medial visual association area, intraparietal sulcus), emphasizing the strong intertwinement of optimistic expectancies and attention deployment. In addition, GMV in the primary visual cortex diminished with increasing optimism robustness, in line with the interpretation of optimism robustness arising from a global, context-oriented perception. Future studies should address the malleability of these structural correlates of optimism robustness. Our results may assist in the identification of treatment targets in depression