Ultrastrong and Hydrophobic Sandwich-Structured MXene-Based Composite Films for High-Efficiency Electromagnetic Interference Shielding.

Electromagnetic interference (EMI) shielding materials are highly necessary to solve the problem of electromagnetic radiation. Transition-metal carbide/nitride (MXene) materials offer great potential for the construction of high-performance EMI shields because of their high electrical conductivity and versatile surface chemistry. However, MXene generally suffers from poor mechanical and oxidation-resistant properties, which hinders its practical applications. Herein, flexible, strong, and hydrophobic sandwich-structured composite films (H-S-MXene), consisting of a conductive MXene layer and supporting aramid nanofiber layer, were fabricated using step-by-step vacuum-assisted filtration and dip coating. Given the unique sandwich structure, hydrogen bonding interactions, and covalent cross-linking of the MXene sheets, the H-S-MXene composite films demonstrated simultaneously excellent EMI shielding and mechanical properties. The EMI shielding effectiveness of the H-S-MXene composite film with 20 wt % MXene content reached 46.1 dB at thickness of 23.2 ± 0.5 µm, and the tensile strength of the film reached 302.1 MPa, which outperformed other reported EMI shielding materials. The excellent mechanical flexibility and hydrophobicity of the H-S-MXene composite films ensured a stable EMI shielding performance, which could withstand cycled bending, torsion, and exposure to aqueous environments. These impressive features made the H-S-MXene composite films promising candidates for electronic devices and aerospace. This study provides important guidance for the rational design of stable MXene-based composites with advanced properties.

Rapid Synthesis of Luotonin A Derivatives via Synergistic Visible-Light Photoredox and Acid Catalysis.

The merging of visible-light photoredox and acid catalysis allowed for an intramolecular Povarov cycloaddition reaction using eosin Y as the photocatalyst and TsOH·H2O as the co-catalyst. A visible-light-promoted dehydrogenative cyclization protocol enabled the construction of Luotonin A derivatives with up to 97% yield.

Layered Foam/Film Polymer Nanocomposites with Highly Efficient EMI Shielding Properties and Ultralow Reflection.

Lightweight, high-efficiency and low reflection electromagnetic interference (EMI) shielding polymer composites are greatly desired for addressing the challenge of ever-increasing electromagnetic pollution. Lightweight layered foam/film PVDF nanocomposites with efficient EMI shielding effectiveness and ultralow reflection power were fabricated by physical foaming. The unique layered foam/film structure was composed of PVDF/SiCnw/MXene (Ti3C2Tx) composite foam as absorption layer and highly conductive PVDF/MWCNT/GnPs composite film as a reflection layer. The foam layer with numerous heterogeneous interfaces developed between the SiC nanowires (SiCnw) and 2D MXene nanosheets imparted superior EM wave attenuation capability. Furthermore, the microcellular structure effectively tuned the impedance matching and prolonged the wave propagating path by internal scattering and multiple reflections. Meanwhile, the highly conductive PVDF/MWCNT/GnPs composite (~ 220 S m-1) exhibited superior reflectivity (R) of 0.95. The tailored structure in the layered foam/film PVDF nanocomposite exhibited an EMI SE of 32.6 dB and a low reflection bandwidth of 4 GHz (R < 0.1) over the Ku-band (12.4 - 18.0 GHz) at a thickness of 1.95 mm. A peak SER of 3.1 × 10-4 dB was obtained which corresponds to only 0.0022% reflection efficiency. In consequence, this study introduces a feasible approach to develop lightweight, high-efficiency EMI shielding materials with ultralow reflection for emerging applications.

Photocatalytic Radical Ortho-Dearomative Cyclization: Access to Spiro[4.5]deca-1,7,9-trien-6-ones.

A highly efficient ortho-dearomative cyclization reaction between alkynes and 2-bromo-2-(2-methoxybenzyl)malonate via visible light-induced photoredox catalysis has been reported. In the presence of 1 mol % fac-Ir(ppy)3, a variety of spiro[4.5]deca-1,7,9-trien-6-ones were obtained in moderate to excellent yields under mild conditions. Under the optimized reaction conditions, a sample reaction of 3 mmol scale proceeded smoothly to give the desired products in 84% yield with a low catalyst loading of 0.1 mol %.

Controllable Fabricating Dielectric-Dielectric SiC@C Core-Shell Nanowires for High-Performance Electromagnetic Wave Attenuation.

Heterostructured dielectric-dielectric nanowires of SiC core and carbon shell (SiC@C) with high-performance electromagnetic wave absorption were synthesized by combining an interfacial in situ polymer encapsulation and carbonization process. This approach overcomes the shortcomings of previous reported methods to prepare carbon shell that both carbon shell and free carbon particles are formed simultaneously. In our developed approach, the core of SiC nanowires are first positively charged. Then the negative resorcinol-formaldehyde polymers as the carbon source are anchored on SiC nanowires under the attraction of electrostatic force, which well suppresses the nucleation of free carbon particles. The thickness of the carbon shell could be modulated from 4 to 20 nm by simply adjusting the moral ratio of resorcinol to SiC nanowires. The resulting SiC@C core-shell nanostructures without free carbon particles offer synergism among the SiC nanowires and the carbon shells, generating multiple dipolar polarization, surfaced polarization, and associated relaxations, which endow SiC@C hybrid nanowires with a minimum reflection loss (RL) value of -50 dB at the frequency of 12 GHz and an effective absorption bandwidth of 8 GHz with RL value under -10 dB at the optimized state. Our results demonstrate that SiC@C hybrid nanowires are promising candidates for electromagnetic wave absorption applications.

Light and Strong Hierarchical Porous SiC Foam for Efficient Electromagnetic Interference Shielding and Thermal Insulation at Elevated Temperatures.

A novel light but strong SiC foam with hierarchical porous architecture was fabricated by using dough as raw material via carbonization followed by carbothermal reduction with silicon source. A significant synergistic effect is achieved by embedding meso- and nanopores in a microsized porous skeleton, which endows the SiC foam with high-performance electromagnetic interference (EMI) shielding, thermal insulation, and mechanical properties. The microsized skeleton withstands high stress. The meso- and nanosized pores enhance multiple reflection of the incident electromagnetic waves and elongate the path of heat transfer. For the hierarchical porous SiC foam with 72.8% porosity, EMI shielding can be higher than 20 dB, and specific EMI effectiveness exceeds 24.8 dB·cm3·g-1 at a frequency of 11 GHz at 25-600 °C, which is 3 times higher than that of dense SiC ceramic. The thermal conductivity reaches as low as 0.02 W·m-1·K-1, which is comparable to that of aerogel. The compressive strength is as high as 9.8 MPa. Given the chemical and high-temperature stability of SiC, the fabricated SiC foam is a promising candidate for modern aircraft and automobile applications.

Consistently high unprotected anal intercourse (UAI) and factors correlated with UAI among men who have sex with men: implication of a serial cross-sectional study in Guangzhou, China.

BACKGROUND: China experiencing an increasing HIV epidemic among men who have sex with men (MSM), and unprotected anal intercourse (UAI) has played a key role in this process. The aims of this study were to examine the trend of UAI and to explore the factors correlated with UAI among MSM in Guangzhou, China. METHODS: Data from 2008 to 2013 were retrieved from the annual serological and behavioral surveys system. We collected information on demographic, HIV related sexual behavior with men and women, access to HIV prevention services, and symptoms of sexually transmitted infections. Chi-square test was used to examine the similarity of the participants during the study period. Univariate and multivariate logistic regression were conducted to test the factors associated with UAI. Trend test was used to check the change of UAI in different characteristic stratums during the study period. RESULTS: In total, 58.4% (range from 54.5% to 62.0%) of the participants reported that they engaged in UAI in the past six months. Participants who aged less than 20 [Adjusted Odds Ratio (AOR): 2.22, 95% Confidential Interval (CI): 1.07-4.61], only attended elementary school (or less) (AOR: 1.41, 95% CI: 1.04-1.90), cohabiting with male partner (AOR: 2.15, 95% CI: 1.66-2.79), divorced or widowed (AOR: 2.80, 95% CI: 1.54-5.07), did not test for HIV in the past year (AOR: 1.36, 95% CI: 1.12-1.65), and had 10 or more partners in the past six months (AOR: 1.85, 95% CI: 1.18-2.91) had higher odds of UAI. However, the proportions of UAI were stable in different stratums during the study period. CONCLUSIONS: The proportion of MSM engaged in UAI was consistently high during the study period. Effective intervention strategies, which include but not limit to risk reduction counseling and testing services, are urgently needed to bring down the risk behaviors of the MSM in Guangzhou, in order to control HIV/STIs epidemic in this specific population.

Increasing HIV and decreasing syphilis prevalence in a context of persistently high unprotected anal intercourse, six consecutive annual surveys among men who have sex with men in Guangzhou, China, 2008 to 2013.

INTRODUCTION: Previous studies have reported a possibly increasing HIV prevalence among men who have sex with men (MSM) in China. However there have been limited systematic analyses of existing surveillance data to learn the trend of HIV prevalence and factors driving the trend. The aims of this study were to examine the trend of HIV prevalence among MSM in Guangzhou and to explore the role of unprotected anal intercourse (UAI) in the trend. METHODS: Snow-ball sampling was applied in the subject recruitment for the annual serological and behavioral surveys among MSM from 2008 to 2013. Data collected in the behavioral survey include demographic information, HIV related sexual behavior with men and women, access to HIV prevention services, and symptoms of sexually transmitted infections. Chi-square test was used to analyze the trend of HIV prevalence. Multivariate logistic regression was conducted to test the factors associated with HIV infection. RESULTS: HIV prevalence increased significantly from 5.0% in 2008 to 11.4% in 2013 while syphilis prevalence decreased from 17.4% to 3.3% in the same period. UAI rates were high and stable in every single year, ranging from 54.5% to 62.0%. Those who were having UAI (OR = 1.80, 95% confidence interval (CI): 1.26-2.58), being migrants, having more than 10 partners, and infected with syphilis had higher risk for HIV infection. CONCLUSIONS: HIV epidemic is expanding in Guangzhou. The persistently high UAI may have played a major role in the increasing trend of HIV prevalence. Targeted prevention program should be conducted among MSM who are migrants, low educational level, syphilis infected, or having multiple partners to encourage HIV test and change UAI behavior. The general high UAI calls for tailored intervention program to promote healthy culture and form a safe sex social norm in the MSM community.

[Detection of intracellular HIV-1 p24 antigen in CD4(+);T cells by flow cytometry and its application for auxiliary diagnosis of HIV-1 infection].

OBJECTIVE: To detect the human immunodeficiency virus 1 (HIV-1) p24 antigen in CD4(+);T cells by flow cytometry (FCM) and assess its application for auxiliary diagnosis of HIV-1 infection. METHODS: CD4(+);T cells from HIV-1-infected individuals and normal controls (negative controls) were detected for intracellular p24 antigen by FCM. Samples from early-HIV-infected individuals were collected, and the intracellular p24 antigen in CD4(+);T cells was detected by FCM. P24 antigen in plasma was detected by ELISA and nucleic acids were tested by nest-PCR. The results of these 3 assays were compared. RESULTS: The rates of p24(+);CD4(+);T cells of the infected individuals were significantly higher than those of the negative controls (P<0.01); the 95th percentile of p24(+);CD4(+);T cell rates of the infected individuals was 1.92% and the cutoff value was 2.00%. Infected individuals with CD4(+);T ≤350 cells/µL had higher p24(+);CD4(+);T cell rates than those with CD4(+);T >350 cells/µL (P<0.05). The detection of p24 antigen in CD4(+);T cells of early-HIV-1-infected patients could identify HIV-1 infection timely, and the detection efficiency of FCM was better than that of the ELISA of p24 antigen in plasma and was equal to that of nucleic acid testing. CONCLUSION: The FCM detection of p24 antigen in CD4(+);T cells could be a promising auxiliary approach for the diagnosis of early HIV-1 infection.

[Cost-effectiveness analysis of HIV testing strategy in hospitals from 2006 to 2010 in Guangzhou].

OBJECTIVE: To evaluate the cost effectiveness of HIV testing strategy in hospitals from 2006 to 2010 in Guangzhou. METHODS: According to the HIV test strategy costs and the number of HIV patients found in Guangzhou, following aspects were calculated as the total cost of HIV testing strategy in hospitals from 2006 to 2010 of Guangzhou, the cost of finding each HIV patient, and the cost of obtaining one quality adjusted life year (QALY) using Markov model. RESULTS: The total HIV test strategy costs increased from 11 106.98 thousand Yuan to 25 105.58 thousand Yuan, and 4599 HIV positive patients were found due to this strategy. The cost-effectiveness of HIV testing were different in hospitals from 2006 to 2010 in Guangzhou. The lowest cost-effectiveness ratio of HIV testing strategy was 11 810 Yuan per HIV positive patient, the highest was 23 510 Yuan, and the average was 16 070 Yuan. According to the Markov model result, 7.2855 QALYs could be gained per HIV patient on average via HIV testing strategy in 113 hospitals in Guangzhou, and the cost of obtaining one QALY was 2210 Yuan. CONCLUSION: The cost effectiveness ratio of HIV testing strategy in hospitals in Guangzhou was significantly lower than the standard of WHO recommended, and it was cost-effective to carry out the HIV testing strategy in Guangzhou.

[Follow-up and outcome as well as the related biological factors on the cases with indeterminate HIV antibody level].

OBJECTIVE: To explore the follow-up visit, outcome and auxiliary diagnosis method on the cases with indeterminate antibody level measured by Western blotting as well as the related biological factors. METHODS: The cases with indeterminate result were followed up according to the National Guideline for Detection of HIV/AIDS (2009) and samples were collected for HIV antibody detection, p24 antigen and nucleic acid were detected as a supplementary diagnosis at the same time. The samples were also be detected for HBV, HCV, TP, HTLV-I/II, ANA, and AFP, and the results were compared to that of screened positive and confirmed negative cases. RESULTS: A total of 73 were followed up successfully and taken a second HIV test, 25 cases were tested positive and 48 were tested negative for HIV during the follow-up period. For the 25 HIV positive cases, the HIV seroconversion rate was 100.00% at any time point when the interval between the first and returning detection was longer than 1 week. The major Western blotting bands for the cases with indeterminate result were p24 and gp160 and it was different between HIV positive and negative cases in Western blotting band profiles. The consistency and sensitivity of nucleic acid detection were higher than 90.00%, and were higher than that of p24 antigen (69.09% (38/55) and 27.27% (6/22)) (χ(2)(consistency) = 6.875, χ(2)(sensitivity) = 18.893, P < 0.05). The positive rates of ANA and AFP of indeterminate cases excluded from HIV infection were 20.83% (10/28) and 6.25% (3/48) and higher than that of screened positive and confirmed negative cases (0.00%), the difference had statistic significance (χ(2)(ANA) = 19.430, χ(2)(AFP) = 5.520, P < 0.05). CONCLUSION: It is critical to get timely diagnosis for the indeterminate cases according to the new national guideline for detection of HIV/AIDS. Nucleic acid detection has higher application value as auxiliary diagnosis for HIV infection than p24 antigen. The increased levels of ANA and AFP may be the factors resulting in the nonspecific indeterminate results.

[Study on the dynamic prevalence of serum antibody against severe acute respiratory syndrome coronavirus in employees from wild animal market in Guangzhou].

OBJECTIVE: To investigate the dynamic trend of specific antibody against severe acute respiratory syndrome (SARS)-CoV in serum collected at various periods among employees in Guangzhou Xinyuan animal market. METHODS: Volunteers from employees of the animal market were recruited and their serum specific antibody against SARS-CoV were determined by enzyme linked immunesorbent assay (ELISA) method. RESULTS: Positive SARS-CoV specific IgG antibody was found 25.61% (n = 328), 13.03% (n = 238), 12.59% (n = 135), 5.04% (n = 139) and 9.43% (n = 53) among volunteers, which were sampled in May 2003, Dec. 2003, Jan. 2004, July 2004 and June 2005 respectively. No specific IgM antibody was found in all of those samples. Among 129 samples which were tested twice or more, 97 were all negative, 18 all positive, 13 changed from positive to negative but only one sample from negative to positive. When the volunteers were divided by the duration of their working experiences as short-term or long-term, those who had worked at animal market for less than or more then 6 months when being tested, the positive rate for long-term employees were relatively constant, however, all of the persons employed after January 2004, when the palm civets and raccoon dogs were culled from the market, were tested negative. CONCLUSION: The prevalence of specific antibody against SARS-CoV in employees of the animal market were somehow related with the presence or absence of palm civet. No serum was tested positive for persons who were employed after palm civets and raccoon dogs were culled from market. This data indicated that the SARS-CoV might have been from the palm civets and raccoon dog, and the animal market seemed to serve as one of the sources of infection.

[Analysis on the risk factors of severe acute respiratory syndromes coronavirus infection in workers from animal markets].

OBJECTIVE: To investigate the possible risk factors of severe acute respiratory syndromes coronavirus (SARS-CoV) infection in workers from animal markets. METHODS: Self-designed questionnaires were used and serum samples were tested. Logistic regression analysis was used to analyze the data. RESULTS: Results from simple factor logistic regression analysis showed that jobs which dealing with domestic livestock, wild livestock, wild animals, aquatics were related to risk factors of SARS-CoV infection. Results from multifactor logistic regression analysis showed that jobs that dealing with wild livestock and poultry were important risk factors with OR 12.28 and 0.41. CONCLUSION: Job that dealing with palm civets was the main risk factor of SARS-CoV infection in animal market workers.