Charpy Impact Test Methods for Cementitious Composites: Review and Commentary

Several researchers have recently employed the Charpy method to characterize the high strain rate mechanical strength of cementitious composites. This paper provides a critical review of existing applications of the Charpy method for impact testing of cementitious composites. Studies have employed various specimen sizes and geometries. Additionally, some studies have tested notched specimens while others have tested plain. Furthermore, varying methods of normalization result in results reported in a variety of incompatible units. The lack of consistency between studies limits the basis for comparison and the ability to validate results, which demonstrates a clear need for a standardized method for Charpy impact testing of cementitious composites. The authors recommend best practices based on sound mechanical principles and existing literature. Finally, the benefits and drawbacks of the Charpy method are discussed and its efficacy is compared with other prevalent methods for impact testing of cementitious composites

Inelastic fingerprints of hydrogen contamination in atomic gold wire systems

We present series of first-principles calculations for both pure and hydrogen contaminated gold wire systems in order to investigate how such impurities can be detected. We show how a single H atom or a single H2 molecule in an atomic gold wire will affect forces and Au-Au atom distances under elongation. We further determine the corresponding evolution of the low-bias conductance as well as the inelastic contributions from vibrations. Our results indicate that the conductance of gold wires is only slightly reduced from the conductance quantum G0=2e^2/h by the presence of a single hydrogen impurity, hence making it difficult to use the conductance itself to distinguish between various configurations. On the other hand, our calculations of the inelastic signals predict significant differences between pure and hydrogen contaminated wires, and, importantly, between atomic and molecular forms of the impurity. A detailed characterization of gold wires with a hydrogen impurity should therefore be possible from the strain dependence of the inelastic signals in the conductance.Comment: 5 pages, 3 figures, Contribution to ICN+T2006, Basel, Switzerland, July-August 200

Scaling Dynamics of Aerosol Coagulation

A combination of static and quasielastic light scattering and the theory of scaling solutions to Smoluchowski\u27s equation was used to determine the absolute coagulation rate K\u270 and kernel homogeneity lambda of a coagulating liquid-drop aerosol. Droplet sizes ranged from 0.23 to 0.42-mu-m, implying Knudsen numbers in the range 0.26 and 0.14. The temporal evolution of the number concentration M0 and the modal radius r(M) of an assumed zeroth-order log-normal distribution showed near-power-law behavior similar to that predicted by the scaling theory. From the temporal scaling behavior of M0(t) and r(M)(t), the absolute coagulation rate was calculated. The coagulation rates from each method were in good agreement. The rate also agreed well with theory that corrected the Brownian rate, good for the continuum regime, by the average Cunningham correction factor. In addition, the time dependence of the moments M0 and r(M), hence the determination of K\u270, was in good agreement with a real-time numerical solution of Smoluchowski\u27s equation for initial conditions analogous to our experimental ones

Spin-independent elastic WIMP scattering and the DAMA annual modulation signal

We discuss the interpretation of the annual modulation signal seen in the DAMA experiment in terms of spin-independent elastic WIMP scattering. Taking into account channeling in the crystal as well as the spectral signature of the modulation signal we find that the low-mass WIMP region consistent with DAMA data is confined to WIMP masses close to $m_\chi \simeq 12$ GeV, in disagreement with the constraints from CDMS and XENON. We conclude that even if channeling is taken into account this interpretation of the DAMA modulation signal is disfavoured. There are no overlap regions in the parameter space at 90% CL and a consistency test gives the probability of $1.2\times 10^{-5}$. We study the robustness of this result with respect to variations of the WIMP velocity distribution in our galaxy, by changing various parameters of the distribution function, and by using the results of a realistic N-body dark matter simulation. We find that only by making rather extreme assumptions regarding halo properties can we obtain agreement between DAMA and CDMS/XENON.Comment: 21 pages, 12 figures, matches version accepted in JCA

Delta chirality ruthenium ‘light-switch’ complexes can bind in the minor groove of DNA with five different binding modes

[Ru(phen)2(dppz)]2+ has been studied since the 1990s due to its “light-switch” properties. It can be used as a luminescent DNA probe, with emission switched on through DNA binding. The luminescence observed is dependent on the solvent accessibility of the pyrazine nitrogen atoms, and therefore is sensitive to changes in both binding site of the cation and chromophore orientation. The compound is also chiral, and there are distinct differences between the enantiomers in terms of the emission behaviour when bound to a variety of DNA sequences. Whilst a number of binary DNA-complex X-ray crystal structures is available, most include the Λ enantiomer, and there is very little structural information about binding of the Δ enantiomer. Here we present the first X-ray crystal structure of a Δ enantiomer bound to well-matched DNA, in the absence of the other, Λ, enantiomer. We show how the binding site observed here can be related to a more general pattern of motifs in the crystallographic literature and propose that the Δ enantiomer can bind with five different binding modes, offering a new hypothesis for the interpretation of solution data

Controlled dehydration of a ruthenium complex-DNA crystal induces reversible DNA kinking

Hydration-dependent DNA deformation has been known since Rosalind Franklin recognised that the relative humidity of the sample had to be maintained to observe a single conformation in DNA fibre diffraction. We now report for the first time the crystal structure, at the atomic level, of a dehydrated form of a DNA duplex and demonstrate the reversible interconversion to the hydrated form at room temperature. This system, containing d(TCGGCGCCGA) in the presence of Λ-[Ru(TAP)2(dppz)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyridophenazine), undergoes a partial transition from an A/B hybrid to the A-DNA conformation, at 84-79% relative humidity. This is accompanied by an increase in kink at the central step from 22° to 51°, with a large movement of the terminal bases forming the intercalation site. This transition is reversible on rehydration. Seven datasets, collected from one crystal at room temperature, show the consequences of dehydration at near-atomic resolution. This result highlights that crystals, traditionally thought of as static systems, are still dynamic and therefore can be the subject of further experimentation

Structural studies reveal the enantiospecific recognition of a DNA G-quadruplex by a ruthenium polypyridyl complex

Using X-ray crystallography, we show an enantiospecificity in DNA G-quadruplex binding, using the complexes Λ/∆-[Ru(TAP)2(dppz-11-CN)]2+ (TAP=1,4,5,8-tetraazaphenanthrene) containing the dppz (dipyridophenazine) ligand, paralleling the specificity of the complexes with duplex DNA. The Λ complex crystallises with the normally parallel stranded d(TAGGGTTA) tetraplex to give the first such antiparallel strand assembly in which syn-guanosine is adjacent to the complex at the 5’ end of the quadruplex core. SRCD measurements confirm that the same conformational switch occurs in solution. The Δ enantiomer, by contrast, is present in the structure but stacked at the ends of the assembly. In addition, we report the structure of Λ-[Ru(phen)2(11-CN-dppz)]2+ bound to d(TCGGCGCCGA), a duplex forming sequence, and use both structural models to aid in the elucidation of the motif-specific luminescence response of the isostructural phen analogue enantiomers

Patient clinical documentation in telehealth environment: Are we collecting appropriate and sufficient information for best practice?

BACKGROUND: During the COVID-19 pandemic, the use of telehealth for patient visits grew rapidly and served an important role as a valuable and necessary resource. Although clinical documentation is critical for telehealth patient visits, there is limited information about how healthcare facilities manage telehealth patient visit documentation, technology used for telehealth visits, and challenges encountered with telehealth patient visit documentation. This study aimed to assess the use of telehealth during the pandemic, the quality of clinical documentation in telehealth practice and to identify challenges and issues encountered with telehealth patient visits in order to develop a strategy for best practices for telehealth documentation and data management. METHODS: Data were collected for this cross-sectional study in January-February 2021 via a self-designed survey of administrators/managers from physicians\u27 offices and mental health facilities. Survey questions included four categories: health organization demographic information; telehealth visits; clinical documentation for telehealth visit; and challenges and barriers related to telehealth documentation technology use. RESULTS: Of 76 respondents, more than half (62%) of the healthcare facilities started using telehealth for patient visits within one year of the onset of the COVID-19 pandemic, with 94% of respondents indicating an increased use of telehealth for patient visits since the pandemic. The most common types of telehealth patient care provided during the pandemic included pediatrics, primary care, cardiology, and women\u27s health. The most consistent data documentation of telehealth visits included: date of service, patient identification number, communication methods, patient informed consent, diagnosis and impression, evaluation results, and recommendations. The telehealth visit data was most commonly used for patient care and clinical practice, billing and reimbursement, quality improvement and patient satisfaction, and administrative planning. The top barriers to telehealth use by the healthcare professionals included patient challenges with telehealth services, such as inequities in quality of technology, lack of patient understanding, and lack of patient satisfaction; this was followed by frustration with constant updates of telehealth guidelines and procedures, understanding required telehealth documentation for reimbursement purposes, payer denial for telehealth visits, and legal and risk issues. CONCLUSIONS: Findings from this study can assist government entities, policymakers, and healthcare organizations in developing and advocating best practices in telehealth usage and clinical documentation improvement strategies