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As a major approach for controlling electromagnetic (EM) waves, metamaterials have experienced an abundant and rapid development in the 21st century. They have provided flexible and powerful techniques for controlling EM waves and brought many unique applications that are difficult to realise with natural materials. With increasing demands on dynamic controls of the EM waves, many innovations have been conducted in both three-dimensional metamaterials and two-dimensional metasurfaces, in which the meta-atom has been gradually evolved from passive to active. In 2014, coding and digital mechanisms were initially introduced to the metamaterials, further advancing the appearance of digitally programmable metamaterials. The programmable metamaterials have shown great potentials in not only real-time manipulations of the EM waves, but also direct information processing on the EM wave level. In this article, we present an in-depth review of the programmable EM metamaterials and metasurfaces, focusing on the programmable features including theoretical concepts, implementing methods and applications in EM controls. We first give a short retrospect of traditional metamaterials and metasurfaces, followed by the concepts and detailed discussions of digital coding and field-programmable metamaterials. Then, we introduce space-domain, time-domain and space–time-domain programmable metamaterials and metasurfaces, mainly focusing on their theories, functionalities, experimental implementations, and system-level applications. Finally, we conclude the current advances of the programmable metamaterials and metasurfaces, and give a prospect for the future developments.
As intense, ultrashort, kHz-repetition-rate laser systems become commercially available, pulse cumulative effects are critical for laser filament-based applications. In this work, the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally. The pulse repetition-rate effect has negligible influence at the leading edge of the filament. Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament. As the repetition rate of the laser pulses increases from 100 to 1000 Hz, the length of the filament extends and the intensity inside the filament increases. A physical picture based on the pulse repetition-rate dependent ‘low-density hole’ effect on filamentation is proposed to explain the obtained results well.
Metamaterials have attracted enormous interests from both physics and engineering communities in the past 20 years, owing to their powerful ability in manipulating electromagnetic waves. However, the functionalities of traditional metamaterials are fixed at the time of fabrication. To control the EM waves dynamically, active components are introduced to the meta-atoms, yielding active metamaterials. Recently, a special kind of active metamaterials, digital coding and programmable metamaterials, are proposed, which can achieve dynamically controllable functionalities using field programmable gate array (FPGA). Most importantly, the digital coding representations of metamaterials set up a bridge between the digital world and physical world, and allow metamaterials to process digital information directly, leading to information metamaterials. In this Element, we review the evolution of information metamaterials, mainly focusing on their basic concepts, design principles, fabrication techniques, experimental measurement and potential applications. Future developments of information metamaterials are also envisioned.
The development of thermoelectric measurement technology at nanoscale is a challenging task. Here, a novel MEMS-based dual temperature control (DTC) measurement method for thermoelectric properties of individual nanowires was proposed. Different from conventional thermal bridge testing devices, this DTC thermoelectric testing device can obtain the thermoelectric properties by independently control ambient temperature and temperature difference between two ends of the nanowires through two separate resistance thermometers without auxiliary heating devices. The reliability of the model and the testing accuracy were verified by accurately measuring the thermal conductivity, electrical conductivity, and the absolute value of the Seebeck coefficient of VO2 nanowires.
The microbiota–gut–brain axis, especially the microbial tryptophan (Trp) biosynthesis and metabolism pathway (MiTBamp), may play a critical role in the pathogenesis of major depressive disorder (MDD). However, studies on the MiTBamp in MDD are lacking. The aim of the present study was to analyze the gut microbiota composition and the MiTBamp in MDD patients.
We performed shotgun metagenomic sequencing of stool samples from 26 MDD patients and 29 healthy controls (HCs). In addition to the microbiota community and the MiTBamp analyses, we also built a classification based on the Random Forests (RF) and Boruta algorithm to identify the gut microbiota as biomarkers for MDD.
The Bacteroidetes abundance was strongly reduced whereas that of Actinobacteria was significantly increased in the MDD patients compared with the abundance in the HCs. Most noteworthy, the MDD patients had increased levels of Bifidobacterium, which is commonly used as a probiotic. Four Kyoto Encyclopedia of Genes and Genomes (KEGG) orthologies (KOs) (K01817, K11358, K01626, K01667) abundances in the MiTBamp were significantly lower in the MDD group. Furthermore, we found a negative correlation between the K01626 abundance and the HAMD scores in the MDD group. Finally, RF classification at the genus level can achieve an area under the receiver operating characteristic curve of 0.890.
The present findings enabled a better understanding of the changes in gut microbiota and the related Trp pathway in MDD. Alterations of the gut microbiota may have the potential as biomarkers for distinguishing MDD patients form HCs.
Patient’s needs and rights are the key to delivering state-of-the-art modern nursing care. It is especially challenging to provide proper nursing care for patients who are reaching the end of life (EOL). In Chinese culture nursing practice, the perception and expectations of these EOL patients are not well known. This article explores the feelings and wishes of 16 terminally ill Chinese cancer patients who are going through the dying process. An open-ended questionnaire with eight items was used to interview 16 terminally ill Chinese cancer patients, and was then analyzed by a combined approach employing grounded theory and interpretive phenomenological analysis. Four dimensions were explored: first, patient’s attitudes towards death, such as accepting the fact calmly, striving to survive, and the desire for control; second, the care desired during the dying process, including avoiding excessive treatment and dying with dignity; third, the degree of the patient’s acceptance of death; and fourth, the consequences of death. This cognitive study offers a fundamental understanding of perceptions of death of terminally ill cancer patients from the Chinese culture. Their attitude toward death was complex. They did not prefer aggressive treatment and most of them had given a great deal of thought to their death.
Despite their importance in the formation and evolution of stellar clusters and galaxies, the formation of high-mass stars remains poorly understood. We recently started a systematic observational study of the 22 GHz water and 44 GHz class I methanol masers in high-mass star-forming regions as a four-year KaVA large program. Our sample consists of 87 high-mass young stellar objects (HM-YSOs) in various evolutionary phases, many of which are associated with two or more different maser species. The primary scientific goals are to measure the spatial distributions and 3-dimensional velocity fields of multiple maser species, and understand the dynamical evolution of HM-YSOs and their circumstellar structures, in conjunction with follow-up observations with JVN/EAVN (6.7 GHz class II methanol masers), VERA, and ALMA. In this paper we present details of our KaVA large program, including the first-year results and observing/data analysis plans for the second year and beyond.
We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona discharge (CD). Fluorescence spectra from neutral and ionic air molecules were measured and compared with pure high-voltage CD and pure laser filamentation (FIL). Among them, high electric field assisted laser FIL produced nitrogen fluorescence more efficiently than either pure CD or pure FIL processes. The nonlinear enhancement of fluorescence from the interaction of the laser filament and corona discharging electric field resulted in a more efficient ionization along the laser filament zone, which was confirmed by the spectroscopic measurement of both ionization-induced fluorescence and plasma-scattered 800 nm laser pulses. This is believed to be the key precursor process for filament-guided discharge.
Galactic cold clumps have been identified from the Planck data (Planck Collaboration, 2011a, 2011b, 2015) as 10 342 cold (7 - 19 K) sources that stand out against a warmer environment, with the Early Cold Cores as a subsample of 915 most reliable detections. There is CO emission associated with the Planck Cold Clumps (PCCs), which has been observed with ground-based radio telescopes at higher resolution (Wu et al. 2012, Liu et al. 2014). A subset of PCCs have also been observed with Herschel at higher resolution (Juvela et al. 2012).
A southern sub-sample of the PCCs has been observed with the Mopra 22-m telescope to study the molecular gas. The Mopra telescope has 3-mm, 7-mm and 12-mm bands, with broadband correlator configuration 8-GHz wide with 0.27-MHz channels, or multiple zoom bands 137-MHz wide with 33-KHz channels, within the 8 GHz.
During the 2013 southern winter season we observed 10 clumps. This included observations in the 3-mm band of 12CO, 13CO and C18O and lines around 89 GHz (e.g. HCN, HCO+ and HNC), in the 7-mm band (e.g. CS) and in the 12-mm band (e.g. NH3). These observations were heterogenous, with sources selected by LST in gaps between observations of other projects, and band chosen by weather (i.e. in conditions unsuitable for higher frequencies, lower frequency bands were observed). During the 2014 season we observed 34 positions in 22 clumps, with zoom mode observations of lines around 89 GHz. This was a more well-defined sample of sources.
The mapping of the CO lines shows good spatial correlation of the CO with the dust column density The CO isotoplogues show high optical depth in 12CO and 13CO. The lines of HCN, HCO+ and HNC are weak, but detected in many of the 2014 sample. We are modelling the line results to determine column densities, excitation temperatures and abundances, using tools such as radex (van der Tak et al. 2007).
To study the molecular environment and feedback of Herbig Ae/Be (HAB) stars, We mapped four HAB stars' nearby region with CO (1-0) and its isotopes by the 13.7m millimeter telescope of Purple Mountain Observatory. The results show that new stars are forming in the nearby molecular cores and HAB stars give them an extra pressure. On the other hand, HAB stars are the main heat source of their surrounding gas.
This paper investigates a 6-degree-of-freedom foldable parallel mechanism for the ship-based stabilized platform, which is driven by closed chain linkages. The velocity and acceleration mappings between the moving platform and inputs of the closed chain linkages are deduced in the form of the first- and second-order influence coefficient matrices. The continuous stiffness matrix is deduced; furthermore, the translation and rotational stiffness along any direction are also deduced. With directional stiffness, the singularity of the mechanism is analyzed, and the explanation of the singularity is given from the viewpoint of stiffness. The directions the platform cannot move or lose its constraints are got from directional stiffness.
We study the enhancement of accuracy, by means of the convolution post-processing technique, for discontinuous Galerkin(DG) approximations to hyperbolic problems. Previous investigations have focused on the superconvergence obtained by this technique for elliptic, time-dependent hyperbolic and convection-diffusion problems. In this paper, we demonstrate that it is possible to extend this post-processing technique to the hyperbolic problems written as the Friedrichs’ systems by using an upwind-like DG method. We prove that the L2-error of the DG solution is of order k+1/2, and further the post-processed DG solution is of order 2k+1 if Qk-polynomials are used. The key element of our analysis is to derive the (2k+1)-order negative norm error estimate. Numerical experiments are provided to illustrate the theoretical analysis.
The environments surrounding nine Wolf-Rayet stars were studied in molecular emission. Expanding shells were detected surrounding these WR stars (see left panels of Figure 1). The average masses and radii of the molecular cores surrounding these WR stars anti-correlate with the WR stellar wind velocities (middle panels of Figure 1), indicating the WR stars has great impact on their environments. The number density of Young Stellar Objects (YSOs) is enhanced in the molecular shells at ∼5 arcmin from the central WR star (lower-right panel of Figure 1). Through detailed studies of the molecular shells and YSOs, we find strong evidences of triggered star formation in the fragmented molecular shells (Liu et al. 2010).
The distribution of alloying elements and the corresponding structural evolution of Mn–Sb alloys in magnetic field gradients were investigated in detail. It was found that a high magnetic field gradient could control the distribution of solute element in the alloys during the solidification process and therefore resulted in the coexistence of both primary MnSb and Sb phases or the aggregation of the primary MnSb with a continuous change in morphology. The positions where these primary phases located depended on the direction of field gradient. The control of the solute element distribution by a high magnetic field gradient was realized through the magnetic buoyancy force that could drive the migration of Mn element in the melt, originating from the difference in the magnetic susceptibility between Mn and Sb. The effectiveness of this control depends on the alloy composition, specimen dimension, cooling rate, and |BdB/dz| value.
Mn-90.8 wt%Sb alloys were solidified without and with high magnetic fields to investigate the effects of high magnetic fields on the structure evolution of the alloys. It was found that there were only MnSb/Sb eutectics without any primary phase in the alloy at 0 T, whereas a small amount of primary MnSb dendrites appeared in the MnSb/Sb eutectic matrix when the magnetic flux density was 4.4 T. In magnetic fields of 6.6, 8.8, and 11.5 T, both of two primary phases, i.e., MnSb and Sb, occurred in the matrix. In addition, the volume fraction of these two primary phases increased with increasing magnetic flux density. In magnetic fields of 8.8 and 11.5 T, primary MnSb dendrites aligned parallel to the magnetic field direction and gathered at the edge of the specimens. In contrast, primary Sb dendrites gathered in the center region of the specimens.
This study is concerned with the investigation of the structural evolution occurring during isothermal annealing of an Mn-89.7 wt%Sb alloy in a high magnetic field in the semisolid state. The alloy specimens were isothermally annealed without and with an 11.5-T magnetic field for various annealing times. With the application of the magnetic field, the average characteristic radius of the primary MnSb particles increased with increasing annealing time. The primary MnSb particles were oriented with their c-plane parallel to the imposed field direction. Furthermore, the primary MnSb particles were found to align along the field direction and form chainlike structures eventually. These phenomena were attributed to the attraction and coalescence of the particles induced by the dipole–dipole interactions among them.
The strategies of repair of tetralogy of Fallot change with the age of patients. In children older than 4 years and adults, the optimal strategy may be to use different method of reconstruction of the right ventricular outflow tract from those followed in younger children, so as to avoid, or reduce, the pulmonary insufficiency that is increasingly known to compromise right ventricular function.
From April, 2001, through May, 2008, we undertook complete repair in 312 patients, 180 male and 132 female, with a mean age of 11.3 years ±0.4 years, and a range from 4 to 48 years, with typical clinical and morphological features of tetralogy of Fallot, including 42 patients with the ventriculo-arterial connection of double outlet right ventricle. The operation was performed under moderate hypothermia using blood cardioplegia. The ventricular septal defect was closed with a Dacron patch. When it was considered necessary to resect the musculature within the right ventricular outflow tract, or perform pulmonary valvotomy, we sought to preserve the function of the pulmonary valve by protecting as far as possible the native leaflets, or creating a folded monocusp of autologous pericardium.
The repair was achieved completely through right atrium in 192, through the right ventricular outflow tract in 83, and through the right atrium, the outflow tract, and the pulmonary trunk in 36 patients. A transjunctional patch was inserted in 169 patients, non-valved in all but 9. There were no differences regarding the periods of aortic cross-clamping or cardiopulmonary bypass. Of the patients, 5 died (1.6%), with no influence noted for the transjunctional patch. Of those having a non-valved patch inserted, three-tenths had pulmonary regurgitation of various degree, while those having a valved patch had minimal pulmonary insufficiency and good right ventricular function postoperatively, this being maintained after follow-up of 8 to 24-months.
Based on our experience, we suggest that the current strategy of repair of tetralogy of Fallot in older children and adults should be based on minimizing the insertion of transjunctional patches, this being indicated only in those with very small ventriculo-pulmonary junctions. If such a patch is necessary, then steps should be taken to preserve the function of the pulmonary valve.
Total body fat mass (TBFM) and total body lean mass (TBLM) are the major components of the human body. Although these highly correlated phenotypic traits are frequently used to characterize obesity, the specific shared genetic factors that influence both traits remain largely unknown. Our study was aimed at identifying common quantitative trait loci (QTLs) contributing to both TBFM and TBLM. We performed a whole genome-linkage scan study in a large sample of 3255 subjects from 420 Caucasian pedigrees. Bivariate linkage analysis was carried out in both the entire sample and gender-specific subsamples. Several potentially important genomic regions that may harbour QTLs important for TBFM and TBLM were identified. For example, 20p12-11 achieved a LOD score of 2·04 in the entire sample and, in the male subsample, two genomic regions, 20p12 (LOD=2·08) and 3p26-25 (LOD=1·92), showed suggestive linkage. In addition, two-point linkage analyses for chromosome X showed suggestive linkages on Xp22 in the entire sample (LOD=2·14) and significant linkage on Xp22 in the female subsample (LOD=3·05). Complete pleiotropy was suggested for 20p12 and 3p26-25 in males. Our results suggest that QTLs on chromosomes 20p12, 3p26-25 and Xp22 may jointly influence TBFM and TBLM. Further fine mapping and gene identification studies for these pleiotropic effects are needed.
To investigate the wheat transcriptional profile under drought stress, a drought-tolerant variety of wheat (Triticum aestivum), Hanxuan 10, was treated with polyethylene glycol (PEG6000) and samples were collected at 0, 1, 6 and 24 h. Complementary DNA was labelled with fluorescent dye and hybridized with the BGI-RiceChip, a whole genome rice gene chip platform, which contains over 60 000 oligos based on the rice genome sequence. Data analysis detected 166, 207 and 328 differentially expressed genes (DGs), respectively, at 1, 6 and 24 h, indicating that the number of DGs increased with the length of the PEG treatment. Functional category analysis showed that the number of DGs related to energy metabolism pathways increased – 4.2%, 8.2% and 16.8%, respectively, as a proportion of the total number of DGs. Most of the photosynthesis-related genes were up-regulated. It is interesting to note that Psbr and ribulose-bisphosphate carboxylase (Rubisco)-coding genes were down-regulated, suggesting their potential role in the response to drought tolerance.
Ni nanowires were fabricated by electrochemical deposition in the pores of alumina filtration membranes, with the diameter around 200nm. To study the magnetic and electrical properties of Ni nanowires, individual nanowire was selected and connected with metal electrodes. Single and multiple constrictions were formed on the nanowires by focused ion beam (FIB). The wires were further thinned using oxygen plasma oxidation. Magnetoresistance curves were studied and compared before and after FIB trimming and oxidization.