Influence of pristine graphene particle sizes on physicochemical, microstructural and mechanical properties of Portland cement mortars

This paper aims to study the effect of the size of pristine graphene (PRG) particles on the compressive and tensile strengths of cement-based mortars and to gain better understandings of the mechanism behind the enhancement of these properties. PRG industrially manufactured by the electrochemical process with a variety of particle sizes including 5 µm, 43 µm, 56 µm, and 73 µm was used at the optimal dosage of 0.07% by weight of cement binder. The results indicate that mechanical strengths of cement mortars at 7 and 28 days considerably depend on the size of PRG. The mixes with size 56 µm and 73 µm show significant influence on both compressive and tensile strengths of cement mortars, which increase approximately 34.3% and 30.1% at 28-day compressive strengths, and 26.9% and 38.6% at 28-day tensile strengths, respectively. On the other hand, the mix with size 43 µm of PRG addition exhibits a significant increase only in tensile strength, and there are no significant effects on either compressive strengths or tensile strengths of the mix containing 5 µm particles. The observed enhancement in the mechanical properties of cement mortars by large PRG sizes is attributed to the improvement of cement hydration level, the reduction of cement particles’ distance in cement gels because of the effect of van der Waals forces between PRG sheets, and the mechanical adhesion forces between PRG sheets and cement gels. The results from this study indicate that PRG is not only a promising additive in practical application for building materials to improve the current drawbacks of cement composites, but also a feasible option to support the reduction of cement mass used in cement composites, which could reduce the CO₂ footprint and amount of CO₂ emission into the atmosphere.Van Dac Ho, Ching-Tai Ng, Togay Ozbakkaloglu, Andy Goodwin, Craig McGuckin, Ramesh U. Karunagaran, Dusan Losi

Time Evolution via S-branes

Using S(pacelike)-branes defined through rolling tachyon solutions, we show how the dynamical formation of D(irichlet)-branes and strings in tachyon condensation can be understood. Specifically we present solutions of S-brane actions illustrating the classical confinement of electric and magnetic flux into fundamental strings and D-branes. The role of S-branes in string theory is further clarified and their RR charges are discussed. In addition, by examining ``boosted'' S-branes, we find what appears to be a surprising dual S-brane description of strings and D-branes, which also indicates that the critical electric field can be considered as a self-dual point in string theory. We also introduce new tachyonic S-branes as Euclidean counterparts to non-BPS branes.Comment: 62 pages, 10 figures. v2 references adde

Demonstration of a novel technique to measure two-photon exchange effects in elastic e±pe^\pm p scattering

The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections. We present the results of a new experimental technique for making direct $e^\pm p$ comparisons, which has the potential to make precise measurements over a broad range in $Q^2$ and scattering angles. We use the Jefferson Lab electron beam and the Hall B photon tagger to generate a clean but untagged photon beam. The photon beam impinges on a converter foil to generate a mixed beam of electrons, positrons, and photons. A chicane is used to separate and recombine the electron and positron beams while the photon beam is stopped by a photon blocker. This provides a combined electron and positron beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen target. The large acceptance CLAS detector is used to identify and reconstruct elastic scattering events, determining both the initial lepton energy and the sign of the scattered lepton. The data were collected in two days with a primary electron beam energy of only 3.3 GeV, limiting the data from this run to smaller values of $Q^2$ and scattering angle. Nonetheless, this measurement yields a data sample for $e^\pm p$ with statistics comparable to those of the best previous measurements. We have shown that we can cleanly identify elastic scattering events and correct for the difference in acceptance for electron and positron scattering. The final ratio of positron to electron scattering: $R=1.027\pm0.005\pm0.05$ for $=0.206$ GeV$^2$ and $0.830\leq \epsilon\leq 0.943$

Multimodal prehabilitation to reduce the incidence of delirium and other adverse events in elderly patients undergoing elective major abdominal surgery: An uncontrolled before-and-after study

Background Delirium is a common and serious complication in elderly patients undergoing major abdominal surgery, with significant adverse outcomes. Successful strategies or therapies to reduce the incidence of delirium are scarce. The objective of this study was to assess the role of prehabilitation in reducing the incidence of delirium in elderly patients. Methods A single-center uncontrolled before-and-after study was conducted, including patients aged 70 years or older who underwent elective abdominal surgery for colorectal carcinoma or an abdominal aortic aneurysm between January 2013 and

Design and construction of the MicroBooNE detector

This paper describes the design and construction of the MicroBooNE liquid argon time projection chamber and associated systems. MicroBooNE is the first phase of the Short Baseline Neutrino program, located at Fermilab, and will utilize the capabilities of liquid argon detectors to examine a rich assortment of physics topics. In this document details of design specifications, assembly procedures, and acceptance tests are reported

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness

Beam-target helicity asymmetry e in K0 Λ and K0 Σ0 photoproduction on the neutron

We report the first measurements of the E beam-target helicity asymmetry for the γ - n - →K0Λ and K0Σ0 channels in the energy range 1.70≤W≤2.34 GeV. The CLAS system at Jefferson Lab uses a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride with low background contamination for the measurements. The multivariate analysis method boosted decision trees is used to isolate the reactions of interest. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin I=0 and I=1 photocoupling transition amplitudes in pseudoscalar meson photoproduction

First measurement of the helicity asymmetry E in eta photoproduction on the proton

Results are presented for the first measurement of the double-polarization helicity asymmetry E for the $\eta$ photoproduction reaction $\gamma p \rightarrow \eta p$. Data were obtained using the FROzen Spin Target (FROST) with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the J\"ulich model to examine the case for the existence of a narrow $N^*$ resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable using that model. Further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances

First measurement of the polarization observable E in the p→(γ→,π⁺)n reaction up to 2.25 GeV

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction $\vec \gamma \vec p \to \pi^+n$, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn-Gatchina, J\"ulich, and SAID groups.Comment: 6 pages, 3 figure