To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Maternal supraphysiological estradiol (E2) environment during pregnancy leads to adverse perinatal outcomes. However, the influence of oocyte exposure to high E2 levels on perinatal outcomes remains unknown. Thus, a retrospective cohort study was conducted to explore the effect of high E2 level induced by controlled ovarian stimulation (COH) on further outcomes after frozen embryo transfer (FET). The study included all FET cycles (n = 10,581) between 2014 and 2017. All cycles were categorized into three groups according to the E2 level on the day of the human Chorionic Gonadotropin trigger. Odds ratios (ORs) and their confidence intervals (CIs) were calculated to evaluate the association between E2 level during COH and pregnancy outcomes and subsequent neonatal outcomes. From our findings, higher E2 level was associated with lower percentage of chemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth as well as increased frequency of early miscarriage. Preterm births were more common among singletons in women with higher E2 level during COH (aOR1 = 1.93, 95% CI: 1.22–3.06; aOR2 = 2.05, 95% CI: 1.33–3.06). Incidence of small for gestational age (SGA) was more common in both singletons (aOR1 = 2.01, 95% CI: 1.30–3.11; aOR2 = 2.51, 95% CI: 1.69–3.74) and multiples (aOR1 = 1.58, 95% CI: 1.03–2.45; aOR2 = 1.99, 95% CI: 1.05–3.84) among women with relatively higher E2 level. No association was found between high E2 level during COH and the percentage of macrosomia or large for gestational age. In summary, oocyte exposure to high E2 level during COH should be brought to our attention, since the pregnancy rate decreasing and the risk of preterm birth and SGA increasing following FET.
Most vibration-based energy harvesters, including piezoelectric harvester system, perform efficiently at only its resonant frequency as linear resonators, usually at very high frequency which are out of the range of frequency of interest. In real life applications, these linear resonators are impractical since real ambient vibrations are simply having varying lower frequencies. Hence, design a tuneable vibration energy harvester at a lower and useful frequency range of interest are essential in allowing promising energy output to meet intended power input at a more practical approach. In this paper, the piezoelectric voltage energy harvester (PVEH) was designed with a flexible fixture with the aim to reduce its first fundamental natural frequency. Two thickness of elastic fixtures were applied to generate power on PVEH. Three experimental techniques were used to measure the vibration characteristics of PVEH. First, the full-field optical technique, amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) measured simultaneously the resonant frequencies and mode shapes. This is followed by the pointwise measurement system, laser Doppler vibrometer (LDV) in which the resonant frequencies were measured by dynamic signal swept-sine analysis. The resonant frequencies and anti-resonant frequencies were also obtained by impedance analysis. The results obtained from experimental measurements were compared with finite element numerical calculation. It is found that the boundary conditions under the elastic fixtures can effectively reduce the resonant frequency of the PVEH with a reasonable voltage output. The fundamental natural frequency of PVEH with the thickness of 0.58-mm elastic fixture is reduced to 37 Hz maintaining at 7.1 volts (1.2 mW), in comparison with the natural frequency on cantilevered PVEH at 78 Hz that produces 7.7 volts (6.5 mW).
Principal component analysis (PCA) is used for dimension reduction and data summary. However, principal components (PCs) cannot be easily interpreted. To interpret PCs, this study compares two methods to approximate PCs. One uses the PCA loadings to understand how input variables are projected to PCs. The other uses forward-stepwise regression to determine the proportions of PC variances explained by input variables.
Two data sets derived from the Canadian Health Measures Survey (CHMS) were used to test the concept of PC approximation: a spirometry subset with the measures from the first trial of spirometry; and, full data set that contained representative variables. Variables were centered and scaled. PCA were conducted with 282 and twenty-three variables respectively. PCs were approximated with two methods.
The first PC (PC1) could explain 12.1 percent and 50.3 percent of total variances in respective data sets. The leading variables explained 89.6 percent and 79.0 percent of the variances of PC1 in respective data sets. It required one and two variables to explain more than 80 percent of the variances of PC1, respectively. Measures related to physical development were the leading variables to approximate PC1 and lung function variables were leading to approximate PC2 in the full data set. The leading variable to approximate PC1 of the spirometry subset were forced expiratory volume (FEV) 0.5/forced vital capacity (FVC) (percent) and FEV1/FVC (percent).
Approximating PCs with input variables were highly feasible and helpful for the interpretation of PCs, especially for the first PCs. This method is also useful to identify major or unique sources of variances in data sets. The variables related to physical development are the variables related to the most variations in the full data set. The leading variable in the spirometry subset, FEV0.5/FVC (percent), is not well studied for its application in clinical use.
Composite measures and indices are used in medical research to represent certain concepts that cannot be measured with one variable. They can be used to predict outcomes or serve as outcomes in trials. The creation of innovative indices is important to increase publications and secure research funding. However, some assumptions and problems are prevalent among indices. We aim to develop a reporting guide and an appraisal tool for indices based on the issues we identified.
We reproduced the three frailty indices from a previous publication and 134,689 principal component-based indices. We reviewed the index assumptions, bias introduced by data processing, relationships between input variables. We interpreted the indices with input variables.
We identified four major issues to be addressed in a reporting guide: constraints imposed by index creation on the input variables; data processing without evidence base; indices poorly linked to input variables; and, relatively inferior predictive power. We demonstrated a flow diagram and a checklist to report and review these four issues related to innovative indices.
A reporting and critical appraisal tool for innovative indices is lacking and needed. These four issues that need to be explicitly considered are previously neglected. This guide is the first attempt to improve the quality and generalizability of innovative indices. This guide can be used to lead further discussion with other experts and review committees.
Principal component analysis (PCA) is important to summarize data or reduce dimensionality. However, one disadvantage of using PCA is the interpretability of the principal components (PCs), especially in a high-dimensional database. This study aims to analyze the patterns of variance accumulation according to PCA loadings and to approximate PCs with input variables from sample data sets.
There were three data sets of various sizes used to understand the performance of PC approximation: Hitters; SF-12v2 subset of the 2004 to 2011 Medical Expenditure Panel Survey (MEPS); and, the full set of 1996 to 2011 MEPS data. The variables in three data sets were first centered and scaled before PCA. PCs approximation was studied with two approaches. First, the PC loadings were squared to estimate the variance contribution by variables to PCs. The other method was to use forward-stepwise regression to approximate PCs with all input variables.
The first few PCs represented large portions of total variances in each data set. Approximating PCs using stepwise regression could more efficiently identify the input variables that explain large portions of PC variances than approximating according to PCA loadings in three data sets. It required few numbers of variables to explain more than eighty percent of the PC variances.
Approximating and interpreting PCs with stepwise regression is highly feasible. Approximating PCs can help i) interpret PCs with input variables, ii) understand the major sources of variances in data sets, iii) select unique sources of information and iv) search and rank input variables according to the proportions of PC variance explained. This is an approach to systematically understand databases and search for variables that are highly representative of databases.
Index mining is a new discipline that aims to search for the composite measures or indices most relevant to the contexts or outcomes. After reviewing three frailty indices and principal component (PC)-based indices, we hereby show certain occasions that can lead to ineffective indices, which consist of bias or fail to represent the theories.
We reproduced and reviewed the three frailty indices and the 134,689 PC (principal component) -based indices from previous publications. The impact of aggregating the input variables on the final indices was analyzed using forward stepwise regression.
Several methods to combine the input variables were related to ineffective projection of information onto the indices. The most common causes leading to ineffective summation of input variables were shown in three examples involving different types of input variables, which were positively or negatively correlated or uncorrelated to the outcome. Ineffective indices were created often because of the summation of redundant information or uncorrelated variables.
The creation of ineffective indices can be avoided if the relationships between input variables and outcomes are properly scrutinized. The creation of composite measures and indices is still a discipline under active development. The three examples we identified are the mistakes that may be repeated unintentionally and need to be addressed with explicit rules. A reporting guide for the creation of composite measures has been proposed. A proper review of index objectives, data characteristics, and data limitations before creating composite measures or indices is recommended.
In this paper, a single-band local surface plasmon mode resonance metamaterial filter is calculated and simulated. The damping constant of the gold film is optimized in simulations to eliminate the effects of the grain boundary and the surface scattering on the transmission property. The transmission property of the designed metamaterial filter can be enhanced through optimizing structural parameters (the vertical distance or radius of the gold particle). Two narrow transmission bands are achieved due to the electric field enhancement effect. The electric field enhancement factor η = |E|/|E0| is used to reveal the electric field resonance strength change. Higher transmission peak and larger field enhancement factor can be achieved than the pure gold hole array structure.
With the rapid development of electronic information and technology, especially the explosive advance of novel electronic devices, ultra-wideband radar detector and satellite communication, the elimination of adverse electromagnetic waves (EWs) effectively is very necessary both for electronic safety and national defense security. As one of the important material basis for controlling adverse EW pollution, compatibility, shielding, and stealth capability of weaponry, microwave absorbing materials has long been an area of intense research activity. Graphene-based materials have attracted great interests for microwave absorption in recent years due to the unique structure and physicochemical properties of graphene, such as high specific surface area, ultrathin thickness, large interface, optical transmittance, and tunable conductive properties, etc. In this paper, the properties and absorption behavior of different kinds of microwave absorbing materials based on graphene were reviewed and discussed in detail. In addition, the perspective of the current challenges and key issues for achieving better microwave absorption performance of the graphene-based materials are provided.
Hypoxia is the primary stimulus for the production of erythropoietin (EPO) in both fetal and adult life. Here, we investigated fetal plasma EPO concentrations in monochorionic (MC) twin pregnancies with selective intrauterine growth restriction (sIUGR) and abnormal umbilical artery (UA) Doppler. We diagnosed sIUGR in presence of (1) birth-weight discordance >20% and (2) either twin with a birth weight <10th percentile. An abnormal UA Doppler was defined as a persistent absent-reverse end diastolic flow (AREDF). The intertwin EPO ratio was calculated as the plasma EPO level of the smaller (or small-for-gestational-age) twin divided by the EPO concentration of the larger (or appropriate-for-gestational-age (AGA)) twin. Thirty-two MC twin pairs were included. Of these, 17 pairs were normal twins (Group 1), seven pairs were twins with sIUGR without UA Doppler abnormalities (Group 2), and eight pairs were twins with sIUGR and UA Doppler abnormalities (Group 3). The highest EPO ratio was identified in Group 3 (p < .001) but no significant differences were observed between Groups 1 and 2. Fetal hemoglobin levels did not differ significantly in the three groups, and fetal EPO concentration did not correlate with gestational age at birth. We conclude that fetal plasma EPO concentrations are selectively increased in MC twin pregnancies with sIUGR and abnormal UA Doppler, possibly as a result of uncompensated hypoxia.
Optimal reinsurance indemnities have widely been studied in the literature, yet the bargaining for optimal prices has remained relatively unexplored. Therefore, the key objective of this paper is to analyze the price of reinsurance contracts. We use a novel way to model the bargaining powers of the insurer and reinsurer, which allows us to generalize the contracts according to the Nash bargaining solution, indifference pricing and the equilibrium contracts. We illustrate these pricing functions by means of inverse-S shaped distortion functions for the insurer and the Value-at-Risk for the reinsurer.
Intermolecular interaction potentials of the acrylamide dimer in 12 equilibrium configurations have been calculated using the second-order Møller-Plesset (MP2) perturbation theory. We have employed Pople’s medium size basis sets [up to 6-311++G(3df,2p)] and Dunning’s correlation consistent basis sets (up to aug-cc-pVTZ). We have also carried out density functional theory (DFT) type calculations and compared the results with those calculated with the MP2 theory.
Dielectric properties of titanium oxide ceramics are strongly influenced by the microstructural features and concentration of dopants and impurity ions. Electrical conductivity (via insulation resistance) of vanadium doped nanostructured titanium dioxide (TiO2) ceramics was measured as a function of donor concentration and temperature. In order to further clarify the effect of the dopants on the microstructural development and resultant dielectric properties of TiO2, electron paramagnetic resonance (EPR) spectroscopy was employed. Vanadium-doped TiO2 exhibited well-defined hyperfine splitting characteristics of the 51V nuclei indicating that the dopant ions are dispersed within the grains and not preferentially segregated at the grain boundaries.
Conventional photonic crystals exhibit low-lying full band gaps for the dielectric contrast smaller than 15. As the dielectric contrast increases, the band gap patterns change characteristics and exhibit interesting properties. In particular, the dispersion curves near the band gap region become concentrated to the middle band frequencies and exhibit an overall red shift in frequency. For a dielectric column photonic crystal made of a hexagonal lattice of circular cylinders, the maximum full band gap was found at the dielectric contrast as high as 27.5, which is attainable by using ceramics materials. The gap opens at high-lying bands, has simultaneous TM and TE band edges, and exhibit flattened dispersion curves near the band edges.
Fluorescent nanodiamonds (FNDs) with a size in the range of 10 – 100 nm have been produced by ion irradiation and annealing, and isolated by differential centrifugation. Single particle spectroscopic characterization with confocal fluorescence microscopy and fluorescence correlation spectroscopy indicates that they are photostable and useful as an alternative to far-red fluorescent proteins for bioimaging applications. We demonstrate the application by performing in vivo imaging of bare and bioconjugated FND particles (100 nm in diameter) in C. elegans and zebrafishes and exploring the interactions between this novel nanomaterial and the model organisms. Our results indicate that FNDs can be delivered to the embryos of both organisms by microinjection and eventually into the hatched larvae in the next generation. No deleterious effects have been observed for the carbon-based nanoparticles in vivo. The high fluorescence brightness, excellent photostability, and nontoxic nature of the nanomaterial have allowed long-term imaging and tracking of embryogenesis in the organisms.
This is a copy of the slides presented at the meeting but not formally written up for the volume.
Current large scale atomistic simulations remain too computationally demanding to be generally applicable to industrial and bioengineering materials. It is desirable to develop multiscale modeling algorithms to perform efficient and informative mesoscopic simulations. Here we present a multipolar expansion method to construct coarse grained force fields (CGFF) for polymer nanostructures and nanocomposites. This model can effectively capture the stereochemical response to anisotropic long-range interactions and can be systematically improved upon adding higher order terms. The coarse-graining procedure forms the basis to perform a hierarchy of multiscale simulations starting with the quantum chemistry calculations to coarse grained molecular dynamics, hopefully toward continuum modeling. We have applied this procedure to molecular clusters such as alkane, benzene, and fullerene. For liquid alkane, molecular dynamics simulations using the CGFF can reproduce the pair distribution functions using atomistic force fields. Molecular mechanics simulations using the CGFF can well reproduce the energetics of benzene clusters from quantum chemistry electronic structure calculations. Subtle anisotropy in the interaction potentials of the fullerene dimer using the Brenner force field can also be well represented by the model. It is promising this procedure can be standardized and further extended.
The electrical characteristics of thin gate dielectrics prepared by low temperature (850 °C) two-step N20 nitridation (LTN) process are presented. The gate oxides were grown by wet oxidation at 800 °C and then annealed in N2O at 850 °C. The oxide with N2O anneal, even for low temperature (850 °C), had nitrogen incorporation at oxide/silicon interface. The charge trapping phenomena and interface-state generation (ΔDitm) induced by constant current stressing were reduced and charge-to-breakdown (Qbd) under constant current stressing was increased. This LTN oxynitride was used as gate dielectric for N-channel MOSFET, whose hot-canrier immunity was shown improved and reverse short channel effect (RSCE) was suppressed.
The vertically aligned carbon nanotubes (CNTs) deposited by microwave plasma-enhanced chemical vapor deposition (MPCVD) were utilized as resistive gas sensors.
The carbon nanotubes were annealed between 200 to 800°C under N2 flow (500 sccm) for 15 minute, respectively. After that, the carbon nanotubes were exposed to an N2 filling and pumping environment. Upon exposure to N2 the electrical resistance of vertically aligned carbon nanotubes was found to increase. It was found that the N2 absorption of unannealed carbon nanotubes was reversible, whereas which of annealing ones was not. However, the sensitivity of the N2 absorption on carbon nanotubes was improved after annealing. From the Raman spectra, the ID/IG ratio of carbon nanotubes also decreased after annealing, indicating that more graphenes were formed by the annealing process. Furthermore, from X-ray photoelectron spectroscopy (XPS), it was observed that the ratio of the oxygen to carbon (O/C) signal intensity increased from 0.094 to 3.943 as the annealing temperature increased. As a consequence, it was suggested that the surface of carbon nanotubes was oxygenated and the absorption of N2 changed from physisorption to chemisorption.
We have performed the finite element simulations to study the binding reaction kinetics of the analyte-ligand protein pairs, C-reactive protein (CRP) and anti-CRP, in a reaction chamber of a biosensor. For diffusion limited reactions, diffusion boundary layers often develop on the reaction surface, thus hindering the reaction. To enhance the efficiency of a biosensor, a non-uniform AC electric field is applied to induce the electrothermal force which stirs the flow field. Biosensors with different arrangements of the electrode pairs and the reaction surface are designed to study the effects of geometric configurations on the binding efficiency. The maximum initial slope of the binding curve can be 6.94 times of the field-free value in the association phase, under an AC field of 15 rms and an operating frequency of 100 kHz. With the electrothermal effect, it is possible to use a slower flow and save much sample consumption without sacrificing the performance of a biosensor. Several design factors not studied in our previous works such as the thermal boundary conditions are discussed.
Intermolecular interaction potentials of the methane dimers have been calculated for 12 symmetric conformations using the Hartree-Fock (HF) self-consistent theory, the second-order M�ller-Plesset (MP2) perturbation theory, and the coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) theory. The HF calculations yield unbound potentials largely due to the exchange-repulsion interaction. In MP2 and CCSD(T) calculations, the basis set effects on the repulsion exponent, the equilibrium bond length, the binding energy, and the asymptotic behavior of the calculated intermolecular potentials have been thoroughly studied. We have employed basis sets from the Slater-type orbitals fitted with Gaussian functions, Pople�s medium size basis sets to Dunning�s correlation consistent basis sets. With increasing basis size, the repulsion exponent and the equilibrium bond length converge at the 6-31G** basis set and the 6-311++G(2d, 2p) basis set, respectively, while a large basis set (aug-cc-pVTZ) is required to converge the binding energy at a chemical accuracy (˜0.01 kcal/mol). We used the BSSE corrected results that systematically converge to the destined potential curve with increasing basis size. The binding energy calculated and the equilibrium bond length using the CCSD(T) method are close to the results at the basis set limit. For molecular dynamics simulation, a 4-site potential model with sites located at the hydrogen atoms was used to fit the ab initio potential data. This model stems from a hydrogen-hydrogen repulsion mechanism to explain the stability of the dimer structure. MD simulations using the ab initio PES show good agreement on both the atom-wise radial distribution functions and the self-diffusion coefficients over a wide range of experimental conditions.