Respiration causes time-varying frequency offsets that can result in ghosting artifacts. We propose a solution, which we term dynamic realtime z-shimming, wherein linear gradients are adjusted dynamically (slice-wise) and in real-time, to reflect mag
netic field inhomogeneities that arise during image acquisition. In dynamic z-shimming, a method that is commonly used to reduce static frequency offsets in MR images of the spinal cord and brain, in-plane (static) frequency offsets are assumed to be homogeneous. Here we investigate whether or not that same assumption can be made for time-varying frequency offsets in the cervical spinal cord region. In order to explore the feasibility of dynamic realtime z-shimming, we acquired images using a pneumatic phantom setup, as well as in-vivo. We then simulated the effects of time-varying frequency offsets on MR images acquired with and without dynamic realtime z-shimming in different scenarios. We found that dynamic realtime z-shimming can reduce ghosting if the time-varying frequency offsets have an in-plane variability (standard deviation) of approximately less than 1 Hz. This scenario was achieved in our phantom setup, where we observed a 50.2% reduction in ghosting within multi-echo gradient echo images acquired with dynamic realtime z-shimming, compared to without. On the other hand, we observed that the in-plane variability of the time-varying frequency offsets is too high within the cervical spinal cord region for dynamic realtime z-shimming to be successful. These results can serve as a guideline and starting point for future dynamic realtime z-shimming experiments in which the in-plane variability of frequency offsets are minimized.
There are several methods to measure computing power. On the other hand, Bit Length (BL) can be considered a metric to measure the strength of an asymmetric encryption method. We review here ways to determine the security, given an span of time, of a
factoring-based encryption method, such as RSA, by establishing a relation between the processing power needed to break a given encryption and the given bit length used in the encryption. This relation would help us provide an estimation of the time span that an encryption method for a given BL will be secure from attacks.
In this paper, we present a concept to fabricate copper based Ti2AlC MAX phase composite focusing on the processing method and the reaction which takes place at the matrix-reinforcement interface to yield 2D TiCx. Copper was reinforced with Ti2AlC (a
gglomerate size ~40 micron) phase and sintered in vacuum by pressure-less sintering. The interface of consolidated samples was investigated using transmission electron microscopy (TEM) to reveal the microstructural details. In the due course of consolidation of Cu-Ti2AlC; the formation of 2D TiCx from the reaction between Cu and Ti2AlC by forming solid solution between Cu and Al was facilitated. The reaction between Cu and Ti2AlC has been elaborated and analyzed in the light of corroborated results. Wavelength dispersive spectroscopy (WDS) throws light on the elemental distribution at the site of interfacial reaction. This investigation elaborates a proof of concept to process an in-situ 2D TiCx reinforced Cu metal matrix composite (MMC).
Topological spin textures in an itinerant ferromagnet, SrRuO$_3$ is studied combining Hall transport measurements and numerical simulations. We observe characteristic signatures of the Topological Hall Effect associated with skyrmions. A relatively l
arge thickness of our films and absence of heavy metal layers make the interfacial Dzyaloshinskii-Moriya interaction an unlikely source of these topological spin textures. Additionally, the transport anomalies exhibit an unprecedented robustness to magnetic field tilting and temperature. Our numerical simulations suggest that this unconventional behavior results from magnetic bubbles with skyrmion topology stabilized by magnetodipolar interactions in an unexpected region of parameter space.
We report on the temperature and electric field driven evolution of the magnetoresistance lineshape at an interface between Ni/AlO$_x$ and Nb-doped SrTiO$_3$. This is manifested as a superposition of the Lorentzian lineshape due to spin accumulation
and a parabolic background related to tunneling anisotropic magnetoresistance (TAMR). The characteristic Lorentzian line shape of the spin voltage is retrieved only at low temperatures and large positive applied bias. This is caused by the reduction of electric field at large positive applied bias which results in a simultaneous reduction of the background TAMR and a sharp enhancement in spin injection. Such mechanisms to tune magnetoresistance are uncommon in conventional semiconductors.
Computing inspired by the human brain requires a massive parallel architecture of low-power consuming elements of which the internal state can be changed. SrTiO3 is a complex oxide that offers rich electronic properties; here Schottky contacts on Nb-
doped SrTiO3 are demonstrated as memristive elements for neuromorphic computing. The electric field at the Schottky interface alters the conductivity of these devices in an analog fashion, which is important for mimicking synaptic plasticity. Promising power consumption and endurance characteristics are observed. The resistance states are shown to emulate the forgetting process of the brain. A charge trapping model is proposed to explain the switching behavior.
In this review we present a theory of cosmological constant and Dark Energy (DE), based on the topological structure of the vacuum. The Multiple Point Principle (MPP) is reviewed. It demonstrates the existence of the two vacua into the SM. The Frogga
tt-Nielsens prediction of the top-quark and Higgs masses is given in the assumption that there exist two degenerate vacua in the SM. This prediction was improved by the next order calculations. We also considered B.G. Sidharths theory of cosmological constant based on the non-commutative geometry of the Planck scale space-time, what gives an extremely small DE density providing the accelerating expansion of the Universe. Theory of two degenerate vacua - the Planck scale phase and Electroweak (EW) phase - also is reviewed, topological defects in these vacua are investigated, also the Compton wavelength phase suggested by B.G. Sidharth was discussed. A general theory of the phase transition and the problem of the vacuum stability in the SM is reviewed. Assuming that the recently discovered at the LHC new resonance with mass $m_S simeq 750$ GeV is a new scalar $S$ bound state $6t + 6bar t$, earlier predicted by C.D. Froggatt, H.B. Nielsen and L.V. Laperashvili, we try to provide the vacuum stability in the SM and exact accuracy of the MPP.
A novel large volume spherical proportional counter, recently developed, is used for neutron measurements. Gas mixtures of $N_{2}$ with $C_{2}H_{6}$ and pure $N_{2}$ are studied for thermal and fast neutron detection, providing a new way for the neut
ron spectroscopy. The neutrons are detected via the ${}^{14}N(n, p)C^{14}$ and ${}^{14}N(n, alpha)B^{11}$ reactions. Here we provide studies of the optimum gas mixture, the gas pressure and the most appropriate high voltage supply on the sensor of the detector in order to achieve the maximum amplification and better resolution. The detector is tested for thermal and fast neutrons detection with a ${}^{252}Cf$ and a ${}^{241}Am-{}^{9}Be$ neutron source. The atmospheric neutrons are successfully measured from thermal up to several MeV, well separated from the cosmic ray background. A comparison of the spherical proportional counter with the current available neutron counters is also given.
Raman forbidden modes and surface defect related Raman features in SnO_2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Due to the weak int
ensities of these peaks, it is difficult to identify these features by using conventional Raman spectroscopy. Tip enhanced Raman spectroscopy (TERS) studies conducted on SnO_2 nanoparticles (NPs) of size 4 and 25 nm have offered significant insights of prevalent defects and disorders. Along with one order enhancement in symmetry allowed Raman modes, new peaks related to disorder and surface defects of SnO_2 NPs were found with significant intensity. Temperature dependent Raman studies were also carried out for these NPs and correlated with the TERS spectra. For quasi-quantum dot sized 4 nm NPs, the TERS study was found to be the best technique to probe the finite size related Raman forbidden modes.
We carried out an experiment in order to obtain the InfraRed (IR) spectra of methyl propionate (CH3CH2COOCH3) in astrochemical conditions and present the IR spectra for future identification of this molecule in the InterStellar Medium (ISM). The expe
rimental IR spectrum is compared with the theoretical spectrum and an attempt was made to assign the observed peak positions to their corresponding molecular vibrations in condensed phase. Moreover, our calculations suggest that methyl propionate must be synthesized efficiently within the complex chemical network of the ISM and therefore be present in cold dust grains, awaiting identification.
