The Egyptian Cardiothoracic Surgeon (ECTS - E-Journal)
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Comment on Driskill and Vrooman: "It's not over 'til the fat lady sings: game-theoretic analysis of sports leagues"
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High speed imaging of dynamic processes with a switched source x-ray CT system
No full textConventional x-ray computed tomography (CT) scanners are limited in their scanning speed by the mechanical constraints of their rotating gantries and as such do not provide the necessary temporal resolution for imaging of fast-moving dynamic processes, such as moving fluid flows. The Real Time Tomography (RTT) system is a family of fast cone beam CT scanners which instead use multiple fixed discrete sources and complete rings of detectors in an offset geometry. We demonstrate the potential of this system for use in the imaging of such high speed dynamic processes and give results using simulated and real experimental data. The unusual scanning geometry results in some challenges in image reconstruction, which are overcome using algebraic iterative reconstruction techniques and explicit regularisation. Through the use of a simple temporal regularisation term and by optimising the source firing pattern, we show that temporal resolution of the system may be increased at the expense of spatial resolution, which may be advantageous in some situations. Results are given showing temporal resolution of approximately 500 μs with simulated data and 3 ms with real experimental data
Phase-locking of bursting neuronal firing to dominant LFP frequency components
No full textNeuronal firing in the hippocampal formation relative to the phase of local field potentials (LFP) has a key role in memory processing and spatial navigation. Firing can be in either tonic or burst mode. Although bursting neurons are common in the hippocampal formation, the characteristics of their locking to LFP phase are not completely understood. We investigated phase-locking properties of bursting neurons using simulations generated by a dual compartmental model of a pyramidal neuron adapted to match the bursting activity in the subiculum of a rat. The model was driven with stochastic input signals containing a power spectral profile consistent with physiologically relevant frequencies observed in LFP. The single spikes and spike bursts fired by the model were locked to a preferred phase of the predominant frequency band where there was a peak in the power of the driving signal. Moreover, the preferred phase of locking shifted with increasing burst size, providing evidence that LFP phase can be encoded by burst size. We also provide initial support for the model results by analysing example data of spontaneous LFP and spiking activity recorded from the subiculum of a single urethane-anaesthetised rat. Subicular neurons fired single spikes, two-spike bursts and larger bursts that locked to a preferred phase of either dominant slow oscillations or theta rhythms within the LFP, according to the model prediction. Both power-modulated phase-locking and gradual shift in the preferred phase of locking as a function of burst size suggest that neurons can use bursts to encode timing information contained in LFP phase into a spike-count code
Increasing the Quantitative Bandwidth of NMR
No full text19F NMR is widely used by chemists in the analysis of drugs and their impurities. Typical drugs have only one or two fluorine atoms, but many protons. Thus in comparison to 1H NMR, 19F NMR offers spectra of significantly reduced complexity, simplifying interpretation. Quantitative analysis using 19F, and other nuclei such as 13C that have wide chemical shift ranges, requires constant-phase broadband excitation over the full spectral width. This can be problematic, since due to the limited radiofrequency power available for pulsed excitation, resonance offset effects distort both signal intensities and signal phases. Because only a small spectral width can be excited uniformly using conventional excitation (e.g. a hard 90° pulse), current practice is to make separate measurements for different regions of the fluorine spectrum, using a quantitation standard with an appropriate chemical shift in each case. This is cumbersome and it can be difficult to find appropriate standards. It would be greatly preferable to find a way to achieve quantitative excitation across the full chemical shift range.To compensate for resonance offset effects, composite and/or shaped pulses are commonly used. However even the best of these methods fall far short of the bandwidths required[1], so swept-frequency “chirp” pulses are needed. In principle, the combination of a 90° and a 180° chirp pulse of appropriate relative amplitude can be used to excite very wide bandwidths[2,3]. Unfortunately, only part of the range excited is usable, because the refocused signal phase still varies in a nonlinear fashion with frequency. A further, hidden, problem is that the signal phase is extremely sensitive to B1 amplitude, so that B1 inhomogeneity causes large (> 30%) losses in signal, even with modern probes. A new broadband sequence, CHORUS (CHirped, ORdered pulses for Ultra-broadband Spectroscopy), has been developed to compensate for this B1¬ sensitivity and to correct the phase errors. CHORUS adds a second 180° chirp pulse, to deliver very uniform, constant-phase excitation over bandwidths of hundreds of kHz, with no undue B1 sensitivity and hence no loss in sensitivity. The accuracies of signal amplitudes and absolute integrals, and their repeatability and robustness, are very satisfactory for quantification purposes; in experimental tests over bandwidths of 100 kHz, drug quantitative analyses showed accuracy and reproducibility better than 1%.Potentially, CHORUS can be a real asset to a range of users, offering much more efficient quantification than simple 90° excitation and allowing a spectrum to be analysed as a whole, with a single standard. For a given RF amplitude, the frequency range over which CHORUS can achieve 98% excitation is about 16 times greater than that for a hard 90° pulse.1. Odedra, S., Thrippleton, M. J. and Wimperis, S., J. Magn. Reson. 225, 81-92, 2012.2. Bohlen, J. M., Rey, M. and Bodenhausen G., J. Magn. Reson. 84, 191-197, 1989.3. Ermakov, V. L., Bohlen, J. M. and Bodenhausen, G., J. Magn. Reson. 103, 226-229, 1993
Small Molecule Inhibition of ERK Dimerization Prevents Tumorigenesis by RAS-ERK Pathway Oncogenes.
No full textNearly 50% of human malignancies exhibit unregulated RAS-ERK signaling; inhibiting it is a valid strategy for antineoplastic intervention. Upon activation, ERK dimerize, which is essential for ERK extranuclear, but not for nuclear, signaling. Here, we describe a small molecule inhibitor for ERK dimerization that, without affecting ERK phosphorylation, forestalls tumorigenesis driven by RAS-ERK pathway oncogenes. This compound is unaffected by resistance mechanisms that hamper classical RAS-ERK pathway inhibitors. Thus, ERK dimerization inhibitors provide the proof of principle for two understudied concepts in cancer therapy: (1) the blockade of sub-localization-specific sub-signals, rather than total signals, as a means of impeding oncogenic RAS-ERK signaling and (2) targeting regulatory protein-protein interactions, rather than catalytic activities, as an approach for producing effective antitumor agents
Shape coexistence in the lead region from a ground-state perspective
No full textGround-state properties are the basis upon which the nuclear levels are built. They are therefore essential building blocks to the understanding of any nuclear phenomenon at low energy, such as shape coexis- tence. Moreover, their study can determine the extent to which shape coexistence leads to the mixing of different configuration. In the region around 186Pb, an extensive laser spectroscopy programme has been undertaken at the CERN ISOLDE radioactive ion beam facility at both the RILIS and CRIS experiments for the study of the even-Z 82Pb and 84Po isotopes, and the odd-Z 79Au, 81Tl, 83Bi, 85At, and 87F