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[Objective] This study is aimed at comprehensively evaluating the soil quality of different vegetation restoration types in the mountainous areas of Beijing, and further identifying the key factors affecting soil quality, so as to provide data support for vegetation restoration and reconstruction in the region. [Methods] The study utilized various vegetation types, including Platycladus orientalis pure forest, Pinus tabulaeformis pure forest, P. orientalis-P. tabulaeformis mixed forest, P. orientalis coniferous and broadleaved mixed forest, P. tabulaeformis coniferous and broadleaved mixed forest, deciduous broad-leaved mixed forest, and non-forest land (CK), with similar stand conditions, as research objects. Fourteen soil physical and chemical indicators were measured to establish the total data set (TDS) for evaluating soil quality. Principal component analysis (PCA) and Pearson correlation analysis were employed to determine the minimum data set (MDS) for soil quality evaluation. Two scoring methods, linear (L) and non-linear (NL), were used to calculate the soil quality index (SQI) and a general linear model (GLM) was employed to identify key factors influencing soil quality. [Results] The bulk density and sand content decreased, while the content of soil nutrients such as organic matter, total nitrogen, total potassium, available nitrogen, and available potassium increased after the vegetation restoration compared with the non-forest land. The screened MDS indicators for soil quality evaluation in the study area were total nitrogen (TN), sand content, total potassium (TK), pH, and available water capacity (AWC). Under the four methods (SQI-LT, SQI-NLT, SQI-LM, and SQI-NLM), the SQI values of different vegetation restoration types were ranked as deciduous broadleaf mixed forest > P. orientalis coniferous and broadleaved mixed forest > P. tabulaeformis pure forest > P. tabulaeformis coniferous and broadleaved mixed forest > P. orientalis-P. tabulaeformis mixed forest > P. orientalis pure forest > non-forest land, and the soil quality significantly improved after vegetation restoration. The soil quality evaluation method of SQI-NLM exhibited better applicability in the mountainous areas of Beijing. Compared with non-forested land, the SQI-NLM of other vegetation restoration types improved by 64%, 48%, 45%, 36%, 33% and 27%, respectively. The GLM model accounted for 85.24% of the total variation in the soil quality index, with vegetation type explaining the largest proportion of the soil quality index (45.09%). [Conclusion] The selection of suitable vegetation restoration types is crucial for improving regional soil quality. In future vegetation restoration efforts, priority should be given to broad-leaved species in tree species selection. Additionally, the choice of silvicultural configuration should depend on the tree species, such as introducing native broad-leaved species into Platycladus orientalis pure forest to form a Platycladus orientalis coniferous and broadleaved mixed forest, or selecting Pinus tabulaeformis pure forest as the optimal silvicultural model.

An analytic model is used to calculate the Raman and fluorescence enhancement of a molecule in between two closely spaced gold nanospheres. Instead of using the conventional approach that only the dipolar plasmonic mode is considered, we calculate the electric field enhancement in the nanometre sized gap, by taking account of the higher order modes in one gold sphere, which couples to the dipolar mode of the other sphere. The experimental confirmation is performed by gap-dependent tip-enhanced Raman spectroscopy (TERS) measurements. The photoluminescence and Raman enhancement are both observed with different growing trends as the gap width decreases. Red-shift of the background spectra is observed and implies the increasing coupling between the nanospheres. This analytic model is shown to be able to interpret the enhancement mechanisms underlying gap-dependent TERS experimental results.

Abstract Transition metal phosphides (TMPs) have been extensively and deeply researched as electrode materials for energy‐related applications. However, the inferior stability is still a bottleneck restricting their substantive development. Herein, a freestanding three‐dimensional hierarchical nanostructure (marked as CC@NC/NiCo‐P) is delicately designed for high‐performance supercapacitors and electrocatalytic hydrogen evolution, where the nitrogen‐doped carbon (NC) layer derived from polydopamine serves as an interface coupling bridge for anchoring electroactive nickel cobalt phosphide (NiCo‐P) nanowire arrays on flexible carbon cloth (CC) substrate. Thanks to the robust interaction between the conductive carbon support and NiCo‐P nanowires, the resultant CC@NC/NiCo‐P electrode delivers an ultrahigh capacitance (2175.5 F/g at 1 A/g) and a distinguished rate capability with a capacity retention of 85.8%. The assembled asymmetric supercapacitor can achieve a superior energy density of 28.47 Wh/kg and an ultralong lifespan of 10 000 cycles. In addition, the CC@NC/NiCo‐P electrode shows favorable electrocatalytic activity toward the hydrogen evolution reaction. These results indicate that the strong binding between the NC layer and metal species in TMPs notably improves the stability and electrochemical activity of CC@NC/NiCo‐P. It is expected that this effective strategy to design innovative electrode materials may be promising for the applications in energy‐related fields.

BackgroundThe global epidemiological situation of COVID-19 remains serious. The rapid hunting of SARS-CoV-2 infection is the key means for preventing transmission.MethodsA total of 40,689 consecutive overseas arrivals were screened for SARS-CoV-2 infection based on PCR and serologic testing. The yield and efficiency of different screening algorithms were evaluated.ResultAmong the 40,689 consecutive overseas arrivals, 56 (0.14%) subjects were confirmed to have SARS-CoV-2 infection. The asymptomatic rate was 76.8%. When the algorithm based on PCR alone was used, the identification yield of a single round of PCR (PCR1) was only 39.3% (95% CI: 26.1–52.5%). It took at least four rounds of PCR to achieve a yield of 92.9% (95% CI: 85.9–99.8%). Fortunately, an algorithm based on a single round of PCR combined with a single round of serologic testing (PCR1+ Ab1) greatly improved the screening yield to 98.2% (95% CI: 94.6–100.0%) and required 42,299 PCR and 40,689 serologic tests that cost 6,052,855 yuan. By achieving a similar yield, the cost of PCR1+ Ab1 was 39.2% of that of four rounds of PCR. For hunting one case in PCR1+ Ab1, 769 PCR and 740 serologic tests were required, costing 110,052 yuan, which was 63.0% of that of the PCR1 algorithm.ConclusionComparing an algorithm based on PCR alone, PCR combined with a serologic testing algorithm greatly improved the yield and efficiency of the identification of SARS-CoV-2 infection.

Abstract The association between pulse pressure and long‐term mortality was investigated among acute coronary syndrome (ACS) patients who received percutaneous coronary intervention (PCI). The study population included 5055 ACS patients in the Department of Cardiology of Beijing Friendship Hospital who were enrolled from January 2013 to July 2019. The median duration of follow‐up was 24 months. Multivariate Cox regression was used to analyze the relationships between PP on inpatient admission and mortalities. Non‐linear associations were studied by restricted cubic splines. Considering the heart function, the analyses were performed in the whole cohort and the LVEF > = 0.5 cohort separately. Subgroup analyses were performed according to the different diagnosis (the myocardial infarction subgroup and the unstable angina pectoris subgroup). When PP was used as categorical variable, the high PP group (≥61 mm Hg) significantly increased the risk of death compared with the intermediate PP group (50–60 mm Hg) in the both cohorts. When PP was used as continuous variable, a U‐shape relationship were found between PP and mortalities in the whole cohort (p (for nonlinearity) = .005 and .003, respectively), with reference PP level of 55 mm Hg. However, this U‐shape relationship disappeared in the LVEF > 0.5 cohort (p (for nonlinearity) = .111 and .117, respectively). The similar results were obtained in MI subgroup. From this study, the U‐shape relationships between PP level and all‐cause and cardiac mortalities were found in ACS patients who underwent PCI. The U‐shape relationships disappeared in the LVEF > 0.5 cohort. The reference PP level was 55 mm Hg.

The carbon fiber/bismaleimide resin composites were prepared by the autoclave molding process. Effects of carbon fiber type and volume fraction of carbon fiber on the high speed impact properties were investigated by air cannon impact testing machine, ultrasonic C-scanner and electronic universal material testing machine. The results demonstrate that the anti-high speed impact property of TZ1000G carbon fiber reinforced composites is superior to that of the CCF300 carbon fiber, CCF700S carbon fiber and CCF800H carbon fiber reinforced composites. Also, the volume fraction of carbon fiber can improve the anti-high speed impact property of the composites. Meanwhile, the results also indicate that failure modes are highly dependent on the impact velocity. Specifically, when the impact velocity is low, a circular pit with fiber delamination appears around on the impact surface of the composites while delamination appears on the back surface along the fiber direction. Also, when the impact velocity is high, a circular hole with fiber delamination around is formed on the impact surface of composites, and the tearing fracture is observed on the back surface.

BackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). Serologic testing is complementary to nucleic acid screening to identify SARS-CoV-2. This study aimed to evaluate unspecific reactivity in SARS-CoV-2 serologic tests.Materials and methodsTotal anti-SARS-CoV-2 antibodies from 46,777 subjects who were screened for SARS-CoV-2 were retrospectively studied to evaluate the incidence and characteristics of the unspecific reactivity. A total of 1,114 pre-pandemic samples were also analysed to compare unspecific reactivity.ResultsThe incidence of unspecific reactivity in anti-SARS-CoV-2 total antibody testing was 0.361% in 46,777 post-pandemic samples, similar to the incidence of 0.359% (4/1,114) in 1,114 pre-pandemic samples (p = 0.990). Subjects ≥ 19 years old had a 2.753-fold [95% confidence interval (CI), 1.130–6.706] higher probability of unspecific reactivity than subjects < 19 years old (p = 0.026). There was no significant difference between the sexes. The unspecific reactivity was associated with 14 categories within the disease spectrum, with three tops being the skin and subcutaneous tissue diseases (0.93%), respiratory system diseases (0.78%) and neoplasms diseases (0.76%). The percentage of patients with a titer ≥ 13.87 cut-off index (COI) in the unspecific reactivity was 7.69%.ConclusionOur results suggest a unspecific reactivity incidence rate of 0.361% involving 14 categories on the disease spectrum. Unspecific reactivity needs to be excluded when performing serologic antibody testing in COVID-19 epidemiological analyses or virus tracing.

Epoxy-matrix composites reinforced by CCF800H, the domestic high strength intermediate modulus carbon fiber, were prepared. Thermoplastic resin was used as the toughening agent of the resin. Through regulating the content of toughening particle in the epoxy resin,effects of the content of toughening agent on the mode-Ⅱ interlaminar fracture toughness of the composite were investigated. The results show that the thermoplastic toughening particles gather at the interlayers of the composite with the filtering effect of the carbon fibers on those particles. The interlayers get thicker with the increasing of the toughening agent. The mode-Ⅱ interlaminar fracture toughness of the composite is increased under the concurrent actions of the toughness and thickness of the interlayer resin.

Graphene aerogels/epoxy composites were prepared by vacuum-impregnated process with graphene aerogels as the functional filler and epoxy resin as polymer matrix. The changes in chemical structure of graphene aerogels during the preparation process and carbonization treatment were investigated by FT-IR, XPS and XRD. The results show that GO@PAA aerogel is prepared by the physical interaction between graphene oxide (GO) and polyamide acid (PAA). PAA will be transformed to polyimide by imidization and graphene oxide is partially reduced during the 300 ℃ thermal treatment. With the carbonation temperature increases, reduction degree of graphene sheets and the carbonation degree of polyimide are increased gradually. Meanwhile, SEM images and OM images show that graphene aerogels can also maintain the good three-dimensional network structure after carbonation treatment and vacuum impregnation. On this basis, graphene aerogels, which serve as the functional filler, taking advantage of the good three-dimensional network structure,can improve the corresponding composites with good electrical property and electromagnetic interference shielding performance. With only 6.23%(mass fraction) graphene aerogels (G@C-1100), the corresponding composites exhibit high electrical conductivity of 252 S·m-1 and an excellent electromagnetic interference shielding effectiveness of 70 dB.

The polyimide fiber/ bismaleimide resin composites were prepared by the autoclave molding process. Effects of volume fraction of polyimide fiber and ambient temperature on the high speed impact properties were investigated using the air cannon impact test. The results demonstrate that the anti-high speed impact property of S35 polyimide fiber reinforced composites is superior to that of TC4 titanium alloy under equal area mass.And polyimide fiber composites have excellent high temperature anti-high speed impact property. Meanwhile, the results also indicate that the volume fraction of polyimide fiber can improve the anti-high speed impact property of the composites. Also, the ballistic energy absorption of polyimide fiber reinforced composites with 73% volume fraction at room temperature can reach 227.0 J, which is 240% higher than that of TC4 titanium alloy under equal area mass. Furthermore, when the impact velocity is low, the composites appear a circular pit with fiber delamination around on the impact surface, while the back surface appears delamination along the fiber direction. Also, when the impact velocity is high, a circular hole with fiber delamination around is formed on the impact surface of composites, and large area fiber delamination along the fiber direction is observed on the back surface.

Graphene/carbon fiber/epoxy composites were prepared by autoclave co-curing molding process with graphene prepregs as the functional layer, which were paved on the surface of carbon fiber perform. The effect of graphene prepregs on the internal quality, electromagnetic interference shielding performance and mechanical properties of the composites was investigated by ultrasound scanner, metallograph, four-probe instrument, vector network analyzer and electronic universal material testing machine. The results show that the internal quality of the graphene/carbon fiber/epoxy composites will not be influenced by the addition of graphene prepregs, and there are a good interfacial compatibility between graphene functional layer and carbon fiber structural layer. On this basis, graphene prepregs, which serves as the functional layer, taking advantage of excellent electrical conductivity, can improve the electromagnetic interference shielding performance of the corresponding composites rapidly. With only one layer of graphene prepreg (G105/3234), electromagnetic interference shielding efficiency of carbon fiber/epoxy composites is improved from 27.7 dB to 64.7 dB. Meanwhile, the obtained composites still maintain satisfactory mechanical properties.

High strength intermediate modulus carbon fiber composites are still the main aviation composites in the world at present and for a long time to come. In recent year, based on the experience of high-strength carbon fiber composites, the industrialization technology of high strength intermediate modulus T800 grade carbon fiber have been broken through in China, and the resin matrix, prepreg and manufacturing process were analysized systematically for the high toughness composites reinforced by Chinese T800 grade carbon fiber. The impact resistance of the resin matrix composites reinforced by Chinese T800H grade carbon fiber is at the same level with that of foreign composites, and the hydrothermal resistance of high toughness epoxy resin matrix composites is better than that of foreign composites with the same CAI level. At the same time, the prepreg of Chinese T800H grade carbon fiber reinforced high toughness composites has excellent process ability, and it can meet the requirements of manual-layup, ATL and AFP. Based on the T800 grade composites, the main research goal is to improve the compression mechanical properties, elastic modulus and CAI based on BVID(barely visible impact damage) for high strength intermediate modulus carbon fiber composites in the future.

Multi-resonant plasmonic simple geometries like nanocylinders and nanorods are highly interesting for two-photon photoluminescence and second harmonic generation applications, due to their easy fabrication and reproducibility in comparison with complex multi-resonant systems like dimers or nanoclusters. We demonstrate experimentally that by using a simple gold nanocylinder we can achieve a double resonantly enhanced two-photon photoluminescence of quantum dots, by matching the excitation wavelength of the quantum dots with a dipolar plasmon mode, while the emission is coupled with a radiative quadrupolar mode. We establish a method to separate experimentally the enhancement factor at the excitation and at the emission wavelengths for this double resonant system. The sensitivity of the spectral positions of the dipolar and quadrupolar plasmon resonances to the ellipticity of the nanocylinders and its impact on the two-photon photoluminescence enhancement are discussed.

With precursor modification by regulating dianhydride hydrolysis degree, the viscosity of polyimide precursor solution, derived from 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and para-phenylenediamine (PDA), was facilely manipulated. The chemical structure of the precursor was characterized by infrared (IR) spectrometry and proton nuclear magnetic resonance (1H-NMR) spectrometry. The effects of dianhydride hydrolysis on the viscosity, imidization process and properties were investigated. The results show that the precursor can be formed from hydrolytic BPDA and PDA, with amide acid and carboxylic ammonium salt groups in the molecular structure. The viscosity of the precursor can be reduced by the introduction of carboxylic ammonium salt group, achieving the effective regulation of viscosity in the 10-105cP range. Importantly, the existence of carboxylic ammonium salt shows no influence on the complete imidization of the precursor, which guarantees the maintenance of mechanical property. Interestingly, the coefficient of thermal expansion (CTE) of this BPDA-PDA polyimide films can be reduced by this viscosity manipulation method.

At the beginning of 2020, the whole world suffered from the new coronavirus (COVID-19). Wearing a mask was believed to reduce the spread of the virus. The core material of a mask required good air permeability and efficient filtration. Electrospun materials may match these requirements. By electrospinning, we prepared polyvinyl butyral (PVB)/berberine hydrochloride (BH) membranes onto the spunbonded nonwovens. The composite meshes showed porous structures, good air permeability (164 ± 16 mm/s) and air filtration efficiency 96.4% for PM 0.3, 100% for PM 2.5, with pressure drop (108 Pa). Moreover, with the addition of BH, the as-spun membranes showed good antibacterial property for staphylococcus aureus. Furthermore, the prepared PVB/berberine membranes had good hydrophobicity with water contact angle higher than 140°. These results indicated that the fabricated PVB/berberine membranes have potential applications in mask and air filtration.

The carbon fiber/epoxy resin composites were prepared by the resin transfer molding (RTM) process. Effect of resin toughness and carbon fiber type on the high speed impact properties was investigated using the air cannon impact test. The effect of high speed impact damage on the residual compressive property of the composites was studied by the compression performance test of the samples which were impacted at high speed. The results demonstrate that the resin toughness can greatly reduce the internal damage degree of composite materials subjected to high speed impact, and can improve the anti-high speed impact property and residual compressive property of the composites. Also, the anti-high speed impact property of T700S carbon fiber reinforced composites is superior to that of the T800H carbon fiber reinforced composites. The results also indicate that failure modes are highly dependent on the impact velocity. Specifically, when the impact velocity is low, the composites appear a circular pit on the impact surface while the back surface appears a convex protrusion. Also, when the impact velocity is high, a circular hole is formed on the impact surface of composites, and the tearing fracture along the fiber direction is observed on the back surface.

Phthalocyanines are frequently used as probing molecules in the field of single-molecule surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). In this work, we systematically compare the SERS and TERS spectra from a thin cobalt phthalocyanine (CoPc) film that is deposited on a Au film. The contributions from electromagnetic (EM), resonance, and charge-transfer enhancements are discussed. Radially and azimuthally polarized vector beams are used to investigate the influences of molecular orientation and the localized surface plasmon resonance (SPR). Furthermore, two different excitation wavelengths (636 and 532 nm) are used to study the resonant excitation effect as well as the involvement of the charge-transfer processes between CoPc and the Au substrate. It is shown that the Raman peaks of CoPc are mostly enhanced by 636 nm excitation through a combination of resonant excitation, high EM enhancement, and chemical enhancement via charge transfer from the metal to the molecule. At 532 nm excitation, however, the SERS and TERS spectra are dominated by photoluminescence, which originates from a photo-induced charge-transfer process from the optically excited molecule to the metal. The contributions of the different enhancement mechanisms explain the optical contrasts seen in the TERS images of Au nanodisks covered by the CoPc film. The insight achieved in this work will help to understand the optical contrast in sub- or single-molecule TERS imaging and apply SERS or TERS in the field of photocatalysis.

The superfine fiber of thermoplastic polyimide(LPI), whose average diameter ranges from 0.36μm to 1.47μm, was prepared through electrospinning with DMAc as solvent. It lays a good foundation for the mass preparation of LPI non-woven. The influence of electrospinning process conditions, including LPI concentration, flow rate and voltage, on morphology of LPI fiber was investigated systematically. The results show that the average diameter increases and the fibers diameter distribution turns wider with the LPI concentration increasing from 22%(mass fraction, same as below) to 30%. Meanwhile, when the concentration is rather lower, some cambiform fibers can be observed. As the concentration increases, the cambiform fiber disappears. While the concentration increases continually, the fibers are adhered to be flakiness. The change of the spinning voltage makes little difference on the average diameter of fibers; the average diameter of fibers increases with the increase of the flow rate of LPI solution; when the flow rate is more than 1.5mL/h, the fibers start to be adhered, the cambiform fibers appear while the flow rate is over 1.8mL/h. Through optimizing the process, the LPI fibers with average diameter of 1.18μm were prepared under 30℃ with the conditions of 28% concentration, 15kV voltage, 1.2mL/h flow rate and the 25cm receiving distance.

The toughened composite was prepared by the domestic high strength medium modulus carbon fiber (CCF800H) reinforced epoxy resin matrix. The influence of different content of toughening thermoplastic within epoxies on the mode-Ⅰ interlaminar fracture toughness (GⅠC) of composites was investigated. The results show the initial strain energy release rate (GⅠC-init) and the propagational strain energy release rate (GⅠC-prop) of composites improve remarkably with the increasing of content of toughening thermoplastics within epoxy matrix. In the case of mass fraction of thermoplastic is greater than 20% of epoxy, the toughening aromatic polyetherimide particle can be concentrated on the interlayer of composite to form the high interlaminar toughness zone. The interlaminar toughened structure constituted by ‘continuous phase’ and ‘dispersion phase’ is fabricated on the interlayer of composite.

Frequency conversion plays an important role in both fundamental and applied nano-optics. Doubling the frequency of light by second harmonic generation (SHG) is a vital process e.g. in laser optics or high-resolution microscopy. SHG can be created through symmetry breaking at plasmonic nanostructures, or the local high electric near-fields of plasmonic nanoantennas can be utilized to further enhance the SHG e.g. from nonlinear crystals. Examples of SHG microscopy using cylindrical vector beams in combination with tilted nanocones and radially symmetric oligomers are shown as well as enhancement studies of the SHG from nonlinear crystals decorated with polarization-matched nanostructures.

In order to solve the problem of high alarming error rate of traditional fire pre-warning algorithms of belt conveyor which alarm according to single characteristic signal, a fire pre-warning algorithm of belt conveyor was proposed which combines the traditional fire alarming algorithms with neural network. The individual characteristic variables extracted by the traditional algorithms are used as inputs of neural network, and the neural network is trained by use of sample data measured in laboratory. The output of the neural network is the final output of the fire pre-warning algorithm. The experimental result showed that the algorithm can effectively identify fire pre-alarming status of the sample data with low error rate.

We evaluated the diversity of soil macrofauna communities inhabiting urban green spaces in Yancheng City, an urbanizing city located east of China. In the end of April 2011, the taxonomic richness, abundance and composition of soil macrofauna communities were assessed and compared among five types of green space (poplar forest, rapeseed farm, grassland in park, lawn and nursery garden) and three depth layers in the soil, with taxonomic resolution attained at the order level. Taxonomic richness (orders) and abundance were significantly different among green spaces. Diversity indices (Margalef's taxonomic richness R and Shannon-Weaver diversity index H') were higher in poplar forest, grassland in park and nursery garden than in rapeseed farm and lawn. Taxonomic richness (Chao 2) showed a similar trend. There were significant effects of green space type and soil layer, which showed a significant interaction affecting macrofauna composition. We recommend that urban green spaces can be used for maintaining biodiversity, not only for landscape purposes.Evaluamos la diversidad de las comunidades de macrofauna del suelo que habitan los espacios verdes urbanos en la ciudad de Yancheng, una ciudad en proceso de urbanización situada al este de China. A fines de abril 2011, la riqueza taxonómica, abundancia y composición de comunidades de macrofauna del suelo fueron evaluadas y comparadas entre cinco tipos de espacio verde (bosque de álamos, granja de colza, pastizal de parque, césped y jardín vivero) y tres capas de profundidad del suelo, con resolución taxonómica a nivel de orden. La riqueza taxonómica (de órdenes) y la abundancia fueron significativamente diferentes entre los espacios verdes. Los indices de diversidad (riqueza taxonómica R de Margalef y diversidad H' de Shannon-Weaver) fueron mayores en el bosque de álamos, pastizal de parque y jardin vivero que en la granja de la colza y el césped. La riqueza taxonómica (Chao 2) mostró una tendencia similar. Hubo efectos significativos del tipo de espacio verde y capa del suelo, los cuales mostraron una interacción significativa afectando la composición de la macrofauna. Recomendamos que los espacios verdes urbanos se puedan utilizar para mantener la biodiversidad, y no solo con propósitos de paisaje.

C21H25NO5, monoclinic, P21/n (no. 14) a = 10.4501(19) Å, b = 15.750(3) Å, c = 12.043(2) Å, β = 102.625(3)°, V = 1934.3(6) Å3, Z = 4, Rgt(F) = 0.0406, wRref(F2) = 0.1177, T = 296(2) K.