Maxwell-compensated design of asymmetric gradient waveforms for tensor-valued diffusion encoding

Purpose: Asymmetric gradient waveforms are attractive for diffusion encoding due to their superior efficiency, however, the asymmetry may cause a residual gradient moment at the end of the encoding. Depending on the experiment setup, this residual moment may cause significant signal bias and image artifacts. The purpose of this study was to develop an asymmetric gradient waveform design for tensor-valued diffusion encoding that is not affected by concomitant gradient. Methods: The Maxwell index was proposed as a scalar invariant that captures the effect of concomitant gradients and was constrained in the numerical optimization to 100 (mT/m)$^2$ms to yield Maxwell-compensated waveforms. The efficacy of this design was tested in an oil phantom, and in a healthy human brain. For reference, waveforms from literature were included in the analysis. Simulations were performed to investigate if the design was valid for a wide range of experiments and if it could predict the signal bias. Results: Maxwell-compensated waveforms showed no signal bias in oil or in the brain. By contrast, several waveforms from literature showed gross signal bias. In the brain, the bias was large enough to markedly affect both signal and parameter maps, and the bias could be accurately predicted by theory. Conclusion: Constraining the Maxwell index in the optimization of asymmetric gradient waveforms yields efficient tensor-valued encoding with concomitant gradients that have a negligible effect on the signal. This waveform design is especially relevant in combination with strong gradients, long encoding times, thick slices, simultaneous multi-slice acquisition and large/oblique FOVs

Passive radar parallel processing using General-Purpose computing on Graphics Processing Units

In the paper an implementation of signal processing chain for a passive radar is presented. The passive radar which was developed at the Warsaw University of Technology, uses FM radio and DVB-T television transmitters as "illuminators of opportunity". As the computational load associated with passive radar processing is very high, NVIDIA CUDA technology has been employed for effective implementation using parallel processing. The paper contains the description of the algorithms implementation and the performance results analysis

Imaging diffusional variance by MRI [public] : The role of tensor-valued diffusion encoding and tissue heterogeneity

Diffusion MRI provides a non-invasive probe of tissue microstructure. We recently proposed a novel method for diffusion-weighted imaging, so-called q-space trajectory encoding, that facilitates tensor-valued diffusion encoding. This method grants access to b-tensors with multiple shapes and enables us to probe previously unexplored aspects of the tissue microstructure. Specifically, we can disentangle diffusional heterogeneity that originates from isotropic and anisotropic tissue structures; we call this diffusional variance decomposition (DIVIDE).In Paper I, we investigated the statistical uncertainty of the total diffusional variance in the healthy brain. We found that the statistical power was heterogeneous between brain regions which needs to be taken into account when interpreting results.In Paper II, we showed how spherical tensor encoding can be used to separate the total diffusional variance into its isotropic and anisotropic components. We also performed initial validation of the parameters in phantoms, and demonstrated that the imaging sequence could be implemented on a high-performance clinical MRI system. In Paper III and V, we explored DIVIDE parameters in healthy brain tissue and tumor tissue. In healthy tissue, we found that diffusion anisotropy can be probed on the microscopic scale, and that metrics of anisotropy on the voxel scale are confounded by the orientation coherence of the microscopic structures. In meningioma and glioma tumors, we found a strong association between anisotropic variance and cell eccentricity, and between isotropic variance and variable cell density. In Paper IV, we developed a method to optimize waveforms for tensor-valued diffusion encoding, and in Paper VI we demonstrated that whole-brain DIVIDE is technically feasible at most MRI systems in clinically feasible scan times

Measurement of single event upsets in the ALICE-TPC front-end electronics

The Time Projection Chamber of the ALICE experiment at the CERN Large Hadron Collider features highly integrated on-detector read-out electronics. It is following the general trend of high energy physics experiments by placing the front-end electronics as close to the detector as possible -- only some 10 cm away from its active volume. Being located close to the beams and the interaction region, the electronics is subject to a moderate radiation load, which allowed us to use commercial off-the-shelf components. However, they needed to be selected and qualified carefully for radiation hardness and means had to be taken to protect their functionality against soft errors, i.e. single event upsets. Here we report on the first measurements of LHC induced radiation effects on ALICE front-end electronics and on how they attest to expectations

To Fold or To Fibrillate? Serendipity in Stability Studies

Proteins are complex structures and years of research have been spent on attempts to understand their complexity. The non-covalent interactions involved in protein folding are: hydrophobic effect, electrostatic interactions, van der Waals interactions and hydrogen bonding. It has been of great interest to address the importance of each of those interactions in proteins. While hydrophobic effect is believed to play the major role in protein folding, Coulombic interactions are of importance in for example protein function, specificity, kinetics and avoidance of unspecific association. Proteins, which are usually folded under native conditions, may also enter other conformations, for example amyloid structures, upon changes in the intrinsic and extrinsic factors. The general objective of this thesis was to study the interplay of the non-covalent interactions in protein folding, assembly and aggregation processes. We found a correlation between stability and assembly of mutants of monellin which implies that the same non-covalent interactions govern the two processes. We also found that the net charge of monellin is important in order to bind to its receptor. In order to stabilize the protein PGB1, we used the split GFP method and selected mutants with elevated melting temperatures by as much as 12˚C. Another series of monellin mutants revealed a correlation between stability and aggregation lag time. In the same study a correlation between predicted aggregation propensity and aggregation lag time was found. We also investigated how terminal extensions of the amino acid sequence affected the aggregation properties of Alzheimer´s β-peptide (Aβ) and found that addition of non-aggregating sequence decreases the aggregation rate of this peptide

From consensus to skepticism? : attitudes of Polish Society towards European Integration

Public opinion surveys conducted in Poland systematically since 2001 confirmed a high, more than 80-per cent, support for our membership in the EU structures. While the need for Poland's membership in the European Union has never been questioned, the issue of the development of European integration has aroused controversy and is still a cause of dispute. The hypothesis of the paper bases on two statements: (1) Polish society attitude towards European integration is more skeptical than would be apparent from the data on general support for EU membership, (2.) Current government, which has established Euroscepticism as the main direction of its foreign policy does not diverge from the mood and social expectations

Why did "the domino effect" not reach Algeria? : limitations and prospects of socio-political transformation

The year 2011 will be one of the most memorable in the modern Arab history because of the wave of revolutions which led to the overthrow of long ruling autocrats in Egypt, Tunisia, Yemen and Libya. Algeria is so far the only country in North Africa that has not experienced sustained mass protests calling for a political change. This paper intends to explain why the Arab Spring has not spread to Algeria? This question becomes apparent bearing in mind that Algeria shares the same explosive factors that have provoked mass revolutions in the neighbouring countries: corruption, disproportion in the regional development, pauperization of society and the lack of civil and political rights. There are several explanations for this "immunity to revolution". First - the fragmentation of Algerian opposition. Second - the fear of the return to the violence which Algerians have lived in for 50 years owing to two brutal conflicts - the war of independence and the civil war of the 90s. Third - the announcement of a raft of political and constitutional reforms by the present regime. Third - the announcement of a raft of political and constitutional reforms by the present regime. Finally, the social peace was brought by the promise to resolve Algeria's long-lasting economic problems starting with unemployment, the promise of implementation of the structural reforms and especially the direct and indirect transfers of public money (rise of salaries, subvention of basic commodities etc.)

THE ROLE AND TASKS OF THE INTERNAL AUDIT AND AUDIT COMMITTEE AS BODIES SUPPORTING EFFECTIVE CORPORATE GOVERNANCE IN INSURANCE SECTOR INSTITUTIONS IN POLAND

Faced with the risk of consecutive waves of financial crisis and economic recession, government committees, financial supervision authorities and financial institutions themselves – both in Poland and worldwide – have launched a number of measures to make the supervision of insurance sector institutions more effective, particularly in aspects related to efficient risk management and internal control. The article describes the impact of the amendment of laws and other regulations on the development of the present internal control systems in insurance sector institutions. It draws attention to the need for a new structure of the internal control system, and the role and purpose of the internal audit and the audit committee as the bodies supporting effective supervision in insurance undertakings and reinsurance undertakings

Diffusional exchange versus microscopic kurtosis from CTI: two conflicting interpretations of the same data

Correlation tensor imaging (CTI) is a new diffusion MRI framework that utilises double diffusion encoding (DDE) to resolve isotropic, anisotropic and microscopic kurtosis sources. Microscopic kurtosis in CTI is provided by the contrast between SDE and parallel DDE signals at the same b-value. Multi-Gaussian exchange (MGE) is a diffusion MRI framework that utilises DDE to measure exchange. The highest exchange sensitivity in MGE is obtained by contrasting SDE and DDE signals at the same b-value. CTI and MGE can thus be applied to analyse the same data but provide conflicting interpretations of that data. We perform Monte Carlo simulations in different geometries with varying levels of exchange to determine which approach is more compatible with the data. Simulations reveal that in all microstructures considered, CTI microscopic kurtosis drastically increases when exchange is introduced. Furthermore, in microstructures that are well-described by the multi-Gaussian assumption, CTI-estimated microscopic kurtosis increases with both the exchange rate and the mixing time, despite fulfilment of the long-mixing-time condition of CTI. Increasing the exchange rate by a factor of 2 positively biases CTI microscopic kurtosis by approximately the same factor. At a modest exchange rate of 10 /s, varying the mixing time from 12 to 100 ms increases CTI microscopic kurtosis by at least a factor of 3. To address this problem, we propose a heuristic approach to combine CTI and MGE to estimate intra-compartmental kurtosis unconfounded by exchange and demonstrate its feasibility using numerical simulations