Application of Raman spectroscopy for tracing the status of silica fume in cementitious materials

Silica fume (SF) is an important component for manufacturing high performance concrete (HPC), owing to its superb pozzolanic reactivity and physical filling effects. However, application of SF in concrete may cause potential hazards issues. Although using SF in slurry form can somehow reduce the potential biotoxicity, the long-term stability and status of the SF particles within cementitious materials is still uncertain. In the current study, attempts were made to use Raman spectroscopy as an innovative alternative technique for tracing and identifying the status of SF both in its original SF slurry and in a 6-month-old hydrated cement paste. Light-optical microscope was also used to examine the morphology of the SF particles in the aforementioned samples. The results showed that under Raman spectroscopy, the various components of the SF in slurry, such as amorphous silica, silicon crystal, and carbon, were clearly recognised. In addition, the SF agglomerates formed in the slurry were also detected. On the other hand, the chemical composition, status, and morphology of both SF and SF agglomerates in the 6-month-old paste were also identified. The study reported in this paper indicates that Raman spectroscopy could be a potential technique for tracing the status of SF, so that the potential safety hazards of SF can be monitored

Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

International audienceUnderstanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.% Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope

Large Component QCD and Theoretical Framework of Heavy Quark Effective Field Theory

Based on a large component QCD derived directly from full QCD by integrating over the small components of quark fields with $|{\bf p}| < E + m_Q$, an alternative quantization procedure is adopted to establish a basic theoretical framework of heavy quark effective field theory (HQEFT) in the sense of effective quantum field theory. The procedure concerns quantum generators of Poincare group, Hilbert and Fock space, anticommutations and velocity super-selection rule, propagator and Feynman rules, finite mass corrections, trivialization of gluon couplings and renormalization of Wilson loop. The Lorentz invariance and discrete symmetries in HQEFT are explicitly illustrated. Some new symmetries in the infinite mass limit are discussed. Weak transition matrix elements and masses of hadrons in HQEFT are well defined to display a manifest spin-flavor symmetry and $1/m_Q$ corrections. A simple trace formulation approach is explicitly demonstrated by using LSZ reduction formula in HQEFT, and shown to be very useful for parameterizing the transition form factors via $1/m_Q$ expansion. As the heavy quark and antiquark fields in HQEFT are treated on the same footing in a fully symmetric way, the quark-antiquark coupling terms naturally appear and play important roles for simplifying the structure of transition matrix elements, and for understanding the concept of `dressed heavy quark' - hadron duality. In the case that the `longitudinal' and `transverse' residual momenta of heavy quark are at the same order of power counting, HQEFT provides a consistent approach for systematically analyzing heavy quark expansion in terms of $1/m_Q$. Some interesting features in applications of HQEFT to heavy hadron systems are briefly outlined.Comment: 59 pages, RevTex, no figures, published versio

Correlation-hole induced paired quantum Hall states in lowest Landau level

A theory is developed for the paired even-denominator fractional quantum Hall states in the lowest Landau level. We show that electrons bind to quantized vortices to form composite fermions, interacting through an exact instantaneous interaction that favors chiral p-wave pairing. Two canonically dual pairing gap functions are related by the bosonic Laughlin wavefunction (Jastraw factor) due to the correlation holes. We find that the ground state is the Moore-Read pfaffian in the long wavelength limit for weak Coulomb interactions, a new pfaffian of an oscillatory pairing function for intermediate interactions, and a Read-Rezayi composite Fermi liquid beyond a critical interaction strength. Our findings are consistent with recent experimental observations of the 1/2 and 1/4 fractional quantum Hall effects in asymmetric wide quantum wells.Comment: 4 pages, 2 figures; published versio

Spin Polarisability of the Nucleon in the Heavy Baryon Effective Field Theory

We have constructed a heavy baryon effective field theory with photon as an external field in accordance with the symmetry requirements similar to the heavy quark effective field theory. By treating the heavy baryon and anti-baryon equally on the same footing in the effective field theory, we have calculated the spin polarisabilities $\gamma_i, i=1...4$ of the nucleon at third order and at fourth-order of the spin-dependent Compton scattering. At leading order (LO), our results agree with the corresponding results of the heavy baryon chiral perturbation theory, at the next-to-leading order(NLO) the results show a large correction to the ones in the heavy baryon chiral perturbation theory due to baryon-antibaryon coupling terms. The low energy theorem is satisfied both at LO and at NLO. The contributions arising from the heavy baryon-antibaryon vertex were found to be significant and the results of the polarisabilities obtained from our theory is much closer to the experimental data.Comment: 21pages, title changed, minimal correction

Calculating Intrinsic and Extrinsic Camera Parameters Based on the PnP Problem

The classical PnP problem is premised on given intrinsic camera parameters. However, for unknown intrinsic camera parameters, given n space points in a world coordinate system and their coordinates in an image coordinate system, the extrinsic camera parameters can be determined. Regarding the existence and uniqueness of a solution for the classical PnP problem, for 4 control points in a plane and an uncalibrated camera, a set of linear equations can be solved based on the correspondence between the space points and the image points. The results show that this approach is feasible and has high calculation precision

Monitoring the cementitious materials subjected to sulfate attack with optical fiber excitation Raman spectroscopy

Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future

MSE-Based Transceiver Designs for Full-Duplex MIMO Cognitive Radios

We study two scenarios of full-duplex (FD) multiple-input-multiple-output cognitive radio networks: FD cognitive ad hoc networks and FD cognitive cellular networks. In FD cognitive ad hoc networks (also referred as interference channels), each pair of secondary users (SUs) operate in FD mode and communicate with each other within the service range of primary users (PUs). Each SU experiences not only self-interference but also interuser interference from all other SUs, and all SUs generate interference on PUs. We address two optimization problems: one is to minimize the sum of mean-squared errors (MSE) of all estimated symbols, and the other is to minimize the maximum per-SU MSE of estimated symbols, both of which are subject to power constraints at SUs and interference constraints projected to each PU. We show that these problems can be cast as a second-order cone programming, and joint design of transceiver matrices can be obtained through an iterative algorithm. Moreover, we show that the proposed algorithm is not only applicable to interference channels but also to FD cellular systems, in which a base station operating in FD mode simultaneously serves multiple uplink and downlink users, and it is shown to outperform HD scheme significantly

MSE based transceiver designs for bi-directional full-duplex MIMO systems

We consider a multiple antenna full-duplex (FD) bidirectional (point-to-point) communication system with a limited analog domain self-interference cancellation capability. The effect of the residual self-interference resulting from independent and identically distributed (i.i.d.) channel estimation errors and limited dynamic ranges of the transmitters and receivers is studied in the digital domain. We design transceiver matrices based on the minimization of sum mean-squared error (MSE) and the maximum per-node MSE optimization problems subject to individual power constraints at each node through an iterative alternating algorithm, which is proven to converge to at least a local optimal solution