Slices taken from the largest type of commercial DC casting ingot were examined to reveal its dendritic features to shed lights on the open questions in the literature related to the effect of grain ...refiners and the convection-induced floating grains on the final grain size distribution in a DC cast ingot. It is found that the ingot comprises globular equiaxed grains featuring coarse secondary dendrite arms and short primary dendrite arms except for a thin chill layer, about 1 mm thick, at its surfaces, featuring fully developed large equiaxed dendrites of long primary dendrite arms and many fine secondary dendrite arms. In the thin chill layer the secondary dendrite arm spacing is smaller by about two times but the grain size, surprisingly, is greater about two times than that in the globular grain zone. Huge floating grains exist at the boundary on the side of the globular grain zone, indicating dendritic fragments are spreading across the entire ingot except for the 1 mm thin chill zone. Such unique features are formed due to the thermal history of grains in the sump. The temperature range in which a floating grain can survive is analyzed and suggested to include temperatures slightly above the liquidus of the alloy. Theories associated with the effect of convection on the formation of dendrites are used to explain the dendritic features in ingots. It appears that the addition of grain refiners produces equiaxed grains only in the chill layer. In the globular grain zone, fragments or floating grains are responsible for the formation of equiaxed grains in DC cast ingots. Since DC casting is the most quiescent metal casting process, grain refinement mechanism associated with the fragmentation and multiplication of dendrites should be considered as dominant mechanisms in grain refining of alloy for gravity casting processes and solidification of an alloy under the influence of external fields.
Experimental data on grain size in hypoeutectic alloys with various solute concentrations are collected and analyzed. Curves of grain size as functions of composition are plotted and compared with ...the relevant phase diagrams. These curves indicate that the minimum in grain size occurs at the solubility limit of the solute on a phase diagram, and the maxima occur at the pure metal and eutectic point where the solidification range of the alloy is zero. The grain size,
d
, is then plotted against phase diagram variables such as the growth restriction factor,
Q
, and the solidification range, Δ
T
. Two-parameter models are proposed to correlate grain size to phase diagram variables. Regression analysis of the experimental data with the two-parameter equations suggests that there is a clear correlation between grain size and the solidification range of the alloy. The linearity of
d
vs
. Δ
T
is much better than that of
d
vs
.
Q
. A grain refinement mechanism based on fragmentation and multiplication of dendrites is used to explain the dependence of
d
on Δ
T
when convection exists in the melt during solidification. Mathematical analysis indicates that the solidification range, Δ
T
, is actually the temperature depression of the planar solid–liquid interface under steady state growth conditions. The temperature depression at the root of a dendrite is proportional to Δ
T
. It is such a temperature depression that causes necking formation at the root of a dendrite. Remelting and fragmentation at the necks could occur due to local temperature fluctuations in the mushy zone in a casting where convection exists in the melt during its solidification.
Chirality, a property of broken mirror symmetry, prevails in nature. Chiral molecules show different biochemical behaviors to their mirror molecules. For left or right circularly polarized lights, ...the fundamental chiral states of electromagnetic fields interact differently with chiral matter, and this effect has been used as a powerful tool for the detection of chiral molecules. This optical sensing, also termed chiral sensing, is not only easy to implement but also non-invasive to the analytes. However, the measurements made by the optical sensing of chiral molecules are challenging, as chiroptical signals are extremely weak. Recent years have seen active research efforts into metamaterial and plasmonic platforms for manipulating local fields to enhance chiroptical signals. This metamaterial approach offers new possibilities of chiral sensing with high sensitivity. Here, we review the recent advances in chiral sensing using metamaterial and plasmonic platforms. In addition, we explain the underlying principles behind the enhancement of chiroptical signals and highlight practically efficient chiral sensing platforms. We also provide perspectives that shed light on design considerations for chiral sensing metamaterials and discuss the possibility of other types of chiral sensing based on resonant metamaterials.
The Purcell effect explains the modification of the spontaneous decay rate of quantum emitters in a resonant cavity. For quantum emitters such as chiral molecules, however, the cavity modification of ...the spontaneous decay rate has been little known. Here we extend Purcell's work to the chiral light-matter interaction in optical resonators and find the differential spontaneous decay rate of chiral molecules coupled to left and right circularly polarized resonator modes. We determine the chiral Purcell factor, which characterizes the ability of optical resonators to enhance chiroptical signals, by the quality factor and the chiral mode volume of a resonator, representing, respectively, the temporal confinement of light and the spatial confinement of the helicity of light. We show that the chiral Purcell effect can be applied to chiroptical spectroscopy. Specifically, we propose a realistic scheme to achieve resonator enhanced chiroptical spectroscopy that uses the double fishnet structure as a nanoscale cuvette supporting the chiral Purcell effect.
Abstract
We present a timing study of the short-period eclipsing cataclysmic variable (CV) HT Cas. Based on new eclipse times derived from our photometric monitoring and archival optical data, ...combined with historical timings, spanning ∼42 yr, we detect a secular decrease in the orbital period at a rate of
P
̇
=
−
1.32
×
10
−
12
ss
−
1
and a cyclic period wiggle with an amplitude of 79.3 s and a period of 30.28 yr. We find that neither gravitational radiation nor magnetic braking can explain the observed decrease rate, suggesting the presence of additional angular momentum loss (AML). The empirical consequential AML (eCAML) model developed by Schreiber et al. can well match the observed orbital decay in HT Cas, and the physical mechanism for eCAML is most likely attributable to the frictional AML following nova eruptions. As for the cyclic variation, the best explanation is the influence of an unseen companion in orbit around the binary. The derived orbital parameters reveal that the hypothetical third body could be a giant planet with mass of
M
3
≃ 14
M
Jup
that is moving on a highly eccentric orbit (
e
= 0.82). Taken together the results of the present study suggest that HT Cas is a unique triple system containing a high-eccentricity giant planet and it has the potential to become an ideal laboratory in which to test models of CV evolution.
A broadband absorber that utilizes a dispersive metamaterial and covers the entire microwave X-band (8–12 GHz) is proposed in the present study. An ideal absorber attached to the surface of a perfect ...electric conductor requires the permittivity of the absorbing layer to be anomalously dispersive in the targeted broad frequency band. We show that anomalous dispersion of the permittivity for the X-band can be fitted to a two-pole Lorentz oscillator model and realized with the use of a double-layered, square-loop metamaterial. We explain the connection between the two-pole oscillator model and the double-layered, square-loop metamaterial using an equivalent circuit model and present explicit design rules for the metamaterial. We fabricate a 4-mm-thick metamaterial absorber with flexible silicon rubber, a resistor element, and conductive wire using carbon and silver conductive ink. Our metamaterial absorber achieves a reflectance of less than −20 dB over the entire X-band region.
The accurate estimation of the tire–road friction coefficient plays a significant role in the vehicle dynamics control. The estimation method should be timely and reliable for the controlling ...requirements, which means the contact friction characteristics between the tire and the road should be recognized before the interference to ensure the safety of the driver and passengers from drifting and losing control. In addition, the estimation method should be stable and feasible for complex maneuvering operations to guarantee the control performance as well. A signal fusion method combining the available signals to estimate the road friction is suggested in this paper on the basis of the estimated ones of braking, driving and steering conditions individually. Through the input characteristics and the states of the vehicle and tires from sensors the maneuvering condition may be recognized, by which the certainty factors of the friction of the three conditions mentioned above may be obtained correspondingly, and then the comprehensive road friction may be calculated. Experimental vehicle tests validate the effectiveness of the proposed method through complex maneuvering operations; the estimated road friction coefficient based on the signal fusion method is relatively timely and accurate to satisfy the control demands.
•Simple method to estimate road friction for ABS, TCS and AYC for ground test.•No extra pressure sensors and other apparatus.•Combine the road friction for ABS, TCS and AYC to improve robustness and accuracy.•Tested under complex maneuvering operations.•Consider the driving and steering combined condition.
Display omitted
•A total of 17 antibiotics were detected in water, sediment (biofilm), organism and feed samples.•Greenhouse ponds were more likely to accumulate antibiotics compared to outdoor ...ponds.•Zn as the coexisting contaminant was significantly correlated with antibiotic concentrations.•Aquaculture wastewater and domestic sewage were potential sources of antibiotics.•Ciprofloxacin and enrofloxacin may present high ecological and resistance risks.
This study focused on the distribution, combined pollution, potential source and risk assessment of 17 antibiotics in an aquaculture ecosystem surrounding the Yellow sea, North China. Antibiotics were detected in various matrices (seawater, sediment/biofilm, organism and feed) in different aquaculture modes (greenhouse and outdoor aquaculture) during the wet and dry seasons in coastal areas of Shandong province. The innovation points of the study were as follows: (1) To the best of our knowledge, this study was one of the few to investigate the occurrence and distribution of antibiotics in mariculture environments along the Yellow Sea coast; (2) Biofilms, a focus of the study, might act as a sink for antibiotics in the aquaculture ecosystem; and (3) The correlation of heavy metals and antibiotic concentrations was proved, which could correspondingly be used as an indicator for antibiotic concentrations in the studied area.
The levels of antibiotics in water were observed to be relatively low, at the ng/L level. Trimethoprim was the most prevalent antibiotic, and was detected in all water samples. Oxytetracycline was detected at high concentrations in biofilms (up to 1478.29 ng/g). Moreover, biofilms exhibited a higher antibiotic accumulation capacity compared to sediments. Concentrations of oxytetracycline and doxycycline were high in feed, while other antibiotics were almost undetected. Tetracycline was widely detected and the concentration of enrofloxacin was highest in organisms.
Correlation analysis demonstrated that environmental parameters and other coexisting contaminants (e.g. heavy metals) significantly affected antibiotic concentrations. In addition, the concentration of Zn was significantly correlated with the total antibiotic concentration and was proportional to several antibiotics in water and sediment (biofilm) samples (p < 0.01). High Mn concentrations were closely related to total and individual (e.g. sulfadiazine, sulfamethazine and enrofloxacin) antibiotic levels, which may result in the combined contamination of the environment. Antibiotics in estuaries and groundwater generally originated from aquaculture wastewater and untreated/treated domestic sewage. Most of the detected antibiotics posed no risk to the environment. Ciprofloxacin and enrofloxacin found in water may present high ecological and resistance risks, while the two antibiotics observed to accumulate in fish may pose a considerable risk to human health through diet consumption. All antibiotics detected in seafood were lower than the respective maximum residue limits. This study can act as a reference for the government for the determination of antibiotic discharge standards in aquaculture wastewater and the establishment of a standardized antibiotic monitoring and management system.
The problem of delay-dependent stability in the mean square sense for stochastic systems with time-varying delays, Markovian switching and nonlinearities is investigated. Both the slowly time-varying ...delays and fast time-varying delays are considered. Based on a linear matrix inequality approach, delay-dependent stability criteria are derived by introducing some relaxation matrices which can be chosen properly to lead to a less conservative result. Numerical examples are given to illustrate the effectiveness of the method and significant improvement of the estimate of stability limit over some existing results in the literature.
PDF
