The dramatically dropped permeability of magnetic materials at gigahertz frequencies, known as the Snoek's limit, has severely constrained the microwave absorbing performance of magnetic materials. ...To break the Snoek's limit at high frequencies, a plate‐like magnetic heterostructure composed of Ni‐Fe ferrite, nitride, and Permalloy is fabricated through nitridation of Ni‐Fe layered double hydroxide. It has been found that single‐phase magnetic flakes or the multi‐phase heterostructure with extraordinarily linked magnetic nanoplates can be obtained by simply adjusting the temperature of nitridation. Due to the highly anisotropic morphology and synergistic effect at abundant heterogeneous interfaces, the magnetic heterostructure shows enhanced imaginary permeability that is even higher than that of single‐phase Permalloy. Accordingly, the magnetic loss in C and X bands is improved, leading to significant enhancement of attenuation constant in this novel microwave absorber. Combined with the moderate permittivity, the impedance matching of the heterostructure is superior compared to every single component, as well as the mixture of these components. As a result, the minimum reflection loss of −59.30 dB at a thickness of 2.02 mm and effective absorption bandwidth (RL<−10 dB) of 2.44 GHz is realized. These findings provide a novel path to designing high‐performance microwave absorbers based on magnetic materials.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
•Blended geopolymers based red mud and coal gangue synthesized through two methods.•Mechanical grinding yielded better activity compared to calcination for the powder mixture.•Two series geopolymer ...both yield excellent mechanical properties.
Two binary geopolymers were prepared from the mixture of low-calcium bayer red mud and kaolinite-based coal gangue. The geopolymers were synthesized using two affordable and feasible methods mainly differed in preactivation and curing processes. The influence of the mix ratio of raw material and alkali activator on the compressive strength properties of two series geopolymers was investigated, and the optimal specimens of which were then determined. Furthermore, a comparative research on the mineral composition, crystal structure and microstructure of the superior geopolymers was performed through XRD, TG-DTA, and SEM-EDXS. Results revealed that GR8G2 was the optimum sample for the series geopolymer I and CR9G1 for geopolymer II. The compressive strength of all samples ranges from 15.05 to 30.25MPa, the geopolymer synthesized from mechanical grinding preactivation displayed better developed strength. Mineral composition and microstructure studies indicated that both the final products are consist of amorphous silica-alumina-based geopolymer gels and some impurity fillers. This study showed that the two geopolymer synthesis methods for red mud and coal gangue were feasible, and the geopolymers may be applied as a new building material. Further studies are necessary to determine the optimal application parameters.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
As promising thermoelectric materials with great stability at high temperature, SrTiO3 based ceramics have attracted much attention, albeit the thermoelectric figure of merit remains relatively low ...for application. To improve the thermoelectric properties, reduced graphene oxide (RGO) is successfully incorporated into Nb-doped SrTiO3 (STNO) ceramics with Sr deficiency via a hetero-aggregation strategy followed by annealing and spark plasma sintering. The addition of RGO enhances the carrier concentration via reduction effect and increases the carrier mobility probably through lowering the double Schottky barrier at grain boundaries, resulting in highly improved electrical conductivity for the composites. Moreover, RGO also stimulates the separation of Nb rich TiO2 phase, which serves as a dispersion with low thermal conductivity to prohibit the phonon transport in the composites. Consequently, a ZT value reaching 0.22 at 800 K for the RGO/STNO nanocomposite is obtained, which is 1.8 times higher compared with the monolithic STNO.
•Nb doped A-site-deficient SrTiO3 composites incorporated with RGO are prepared.•RGO leads to reduced grain size and separated Nb rich TiO2 phase.•RGO lowers the double Schottky barrier and increases electrical conductivity.•The thermal conductivity is depressed by TiO2 phase and fine microstructure.•ZT of composite is 1.8 times higher compared to the monolithic ceramic.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The value of right atrial (RA) function in cardiovascular diseases is currently limited. This study was to explore the prognostic value of RA strain derived from fast long axis method by ...cardiovascular magnetic resonance (CMR) in patients with non-ischemic dilated cardiomyopathy (DCM).
We prospectively enrolled patients with DCM who underwent CMR from June 2012 to March 2019 and 120 age- and sex-matched healthy subjects. Fast long-axis strain method was performed to assess the RA phasic function including RA reservoir strain, conduit strain, and booster strain. The predefined primary endpoint was all-cause mortality. The composite heart failure (HF) endpoint included HF death, HF readmission, and heart transplantation. Cox regression analysis and Kaplan-Meier survival curve were performed to describe the association between RA strain and outcomes.
A total of 624 patients (444 men, mean 48 years) were studied. After a median follow-up of 32.5 months, 116 patients (18.6%) experienced all-cause mortality and 205 patients (32.9%) reached composite HF endpoint. RA function was impaired in DCM patients compared with healthy subjects (all P < 0.001). After adjustment for covariates, RA reservoir strain hazard ratio (HR) (per 5% decrease) 1.19, 95% confidence interval (CI) 1.03-1.37, P = 0.022 and conduit strain HR (per 5% decrease) 1.37, 95% CI 1.03-1.84, P = 0.033 were independent predictors of all-cause mortality. Moreover, RA strain added incremental prognostic value for the prediction of adverse cardiac events over baseline clinical and CMR predictors (all P < 0.05).
RA strain by fast long-axis analysis is independently associated with adverse clinical outcomes in patients with DCM.
Trial registration number: ChiCTR1800017058; Date of registration: 2018-07-10 (Retrospective registration); URL: https://www.
gov.
Full text
Available for:
DOBA, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, UILJ, UKNU, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Graphene is an ultra-thin, remarkably flexible and highly stiff 2D material that can profoundly change the microstructure of composite as filler phase, giving rise to mechanical properties greatly ...different from traditional composites. However, there are very few examples that demonstrate the exceptional properties in graphene based ceramic composite because of the tradeoff between small thickness of graphene platelet and dispersion uniformity in processing. Here, a fully dense Al2O3 composite with uniformly dispersed few-layer graphene (FLG) is prepared by heteroaggregation technique and spark plasma sintering. It is found that in comparison to monolithic Al2O3, drastically reduced Young’s modulus (298GPa), completely retained fracture strength (417MPa) and enhanced fracture toughness (5.3MPam1/2) are simultaneously realized in this composite, leading to an unprecedented increase of strain tolerance by ∼40% at merely 2.18vol.% of filler loading. It is believed that the unique highly wrinkled structure of FLG at triple junctions of ceramic matrix causes the inefficient load transfer before crack initiation and thus low stiffness in composite. Whereas after crack initiation, by the “stretched filler bridging” of FLG platelet behind crack tip, the toughness of composite is enhanced so that the high fracture strength can be retained.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Despite the attractive thermoelectric properties in single crystals, the fabrication of high-performance polycrystalline SnSe by a cost-effective strategy remains challenging. In this study, we ...prepare the undoped SnSe ceramic with remarkable thermoelectric efficiency by the combination of a cold sintering process (CSP) and thermal annealing. The high sintering pressure during CSP induces not only highly oriented grains but also a high concentration of lattice dislocations and stacking faults, which leads to large lattice strain that can shorten the phonon relaxation time. Meanwhile, the thermal annealing breaks the highly resistive SnO x layers at grain boundaries, which improves the electrical conductivity and power factor. In addition, the grain growth during annealing further turns the broken SnO x layers into nanoparticles, which further lowers the thermal conductivity by enhanced scattering. As a result, a peak ZT of 1.3 at 890 K and a high average ZT of 0.69 are achieved in the polycrystalline SnSe, suggesting great potential in mid-temperature power generation. This work may pave the way for the mass production of SnSe-based ceramics for thermoelectric devices.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Dispersing the Ce3+ doped yttrium aluminum garnet (Ce:YAG) phosphor in the glass matrix has been widely investigated to replace conventional organic resin or silicone packaging. However, the reaction ...layer formed between commercial phosphors and glass matrix severely degrades the optical performance of Ce:YAG phosphor in silica glass (PiSG) materials. This paper demonstrates an ultra-fast method for preparing high performance PiSG materials. Instead of traditional melting process, the highly transparent PiSG samples can be rapidly fabricated from mixtures of commercial Ce:YAG phosphor and mesoporous SiO2 (SBA-15) powders using spark plasma sintering (SPS) at relatively low temperature (1000 °C) within short time (10 min). Owing to the inhibition of the deleterious interface reactions between Ce:YAG phosphor and silica glass matrix, the phosphor has been perfectly preserved, and the internal relative quantum yield of the PiSG sample reaches as high as 93.5% when excited at 455 nm, which is the highest efficiency in current research. Furthermore, combining the PiSG sample, we successfully fabricate a light-emitting diode (LED) module exhibiting a superior performance with luminous efficacy of 127.9 lm/W, correlated color temperature of 5877 K and color rendering index of 69 at the operating current of 120 mA. This work on the high performance LED modules provides not only a new approach to fabricate the functional glass-based materials that is sensitive to the high temperature, but also a possibility to extend the lifetime and improve the optical performances of the glass based LEDs.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Graphene oxide/ZnO ceramic composites with highly preserved pristine structure of filler are prepared via cold sintering technology.•Moderate complex permittivity and good impedance matching lead to ...highly improved microwave absorbing performance in cold sintered composites compared to the spark plasma sintered ones.•Both flexural strength and hardness of the graphene oxide reinforced composites are enhanced remarkably compared to the cold sintered pure ZnO.
The abruptly increased dielectric loss in graphene oxide (GO) induced by high-temperature sintering has prevented GO from being used as an absorbent in ceramic-matrix microwave absorbing composites (MACs). Here, we show the first example that the pristine structure of GO can be largely preserved in ceramic composite by using cold sintering technology. Compared with the composites densified by ordinary spark plasma sintering, cold sintered samples possess lower complex permittivity and superior impedance matching. Therefore, the cold sintered ZnO composite with 0.50 wt% GO loading shows the minimum reflection loss of -47.5 dB at thickness of 3.2 mm, and the effective absorption bandwidth of 4.4 GHz at thickness of 1.7 mm. Moreover, both flexural strength and hardness of the cold sintered composite are improved considerably compared to the monolithic cold sintered ZnO. These findings imply that cold sintering enables the thermally unstable materials to be applied in highly effective MACs with robust mechanical performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For years, most of the advanced polycrystalline thermoelectric (TE) materials are fabricated by spark plasma sintering (SPS) in the research field, mainly because of its high processing efficiency. ...However, issues like high energy consumption and an expensive apparatus have prevented the application of this strategy in industry. Herein, taking PbTe0.94Se0.06 (PTS) as a typical n-type mid-temperature material, we demonstrate that the cold sintering process (CSP) can serve as a green and cost-effective technology for preparing advanced TE materials. By selecting the solvothermal precursors as liquid sintering aids, the CSP-densified PTS shows a maximum figure of merit of 0.96 at 700 K, which is on par with, if not better than, the reported similar materials prepared by SPS. This remarkable performance is ascribed to the distinct densification procedure in the CSP: (1) the ultralow temperature alleviates the precipitation of Pb, which preserves the high carrier concentration of PTS; (2) the transient liquid phase forms intimate grain boundaries comparable to the high-temperature sintered one, leading to a high carrier mobility; (3) the dissolution–precipitation process greatly restrains the coarsening of precipitates, which effectively suppresses the bipolar effect and lattice thermal conductivity due to enhanced scattering. We believe that these results can greatly encourage the application of CSP in the future development of TE materials.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Objectives
The non-invasive assessment of left ventricular (LV) diastolic dysfunction remains a challenge. The role of first-pass perfusion cardiac magnetic resonance (CMR) parameters in quantitative ...hemodynamic analyses has been reported. We therefore aimed to validate the diagnostic ability and accuracy of such parameters against cardiac catheterization for LV diastolic dysfunction in patients with left heart disease (LHD).
Methods
We retrospectively enrolled 77 LHD patients who underwent CMR imaging and cardiac catheterization. LV diastolic dysfunction was defined as pulmonary capillary wedge pressure (PCWP) or LV end-diastolic pressure (LVEDP) > 12 mmHg on catheterization. On first-pass perfusion CMR imaging, pulmonary transit time (PTT) was measured as the time for blood to pass from the left ventricle to the right ventricle (RV) through the pulmonary vasculature. Pulmonary transit beat (PTB) was the number of cardiac cycles within the interval, and pulmonary blood volume indexed to body surface area (PBVi) was the product of PTB and RV stroke volume index (RVSVi).
Results
Of the 77 LHD patients, 53 (68.83%) were found to have LV diastolic dysfunction, and showed significantly higher PTTc, PTB, and PBVi (
p
< 0.05) compared with those without. In multivariate analyses, only PTTc and PTB were identified as independent predictors of LV diastolic dysfunction (
p
< 0.05). With an optimal cutoff of 11.9 s, PTTc yielded the best diagnostic performance for LV diastolic dysfunction (area under the curve = 0.83,
p
< 0.001).
Conclusions
PTTc may represent a non-invasive quantitative surrogate marker for the detection and assessment of diastolic dysfunction in LHD patients.
Key Points
• PTTc yielded the best diagnostic accuracy for diastolic dysfunction, with an optimal cutoff of 11.9 s, and a specificity of 100%.
• PTTc and PTB were found to be independent predictors of LV diastolic dysfunction across different multivariate models with high reproducibility.
• PTTc is a promising non-invasive surrogate marker for the detection and assessment of diastolic dysfunction in LHD patients.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, VSZLJ, ZAGLJ
