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Xiumei Liu

Publications and source records attributed to Xiumei Liu.

At least 19 recordsLinked to original sources
PubMed2026

Integrated physiological and transcriptomic analyses reveal coordinated gill responses to heat stress in pikeperch (Sander lucioperca).

Climate change-driven warming of aquatic environments has made thermal stress an increasingly important factor influencing fish physiological homeostasis. Given their central roles in respiration and osmoregulation, gills are particularly responsive to variations in ambient temperature. Histological examination, physiological measurements, and transcriptome profiling were integrated to investigate the mechanisms associated with heat stress-induced gill injury in pikeperch (Sander lucioperca). Histological analysis revealed that exposure to 29 °C directly caused structural damage to the gills of pikeperch. Oxidative status was evaluated by measuring malondialdehyde (MDA) levels and the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). MDA accumulation was significantly enhanced under heat stress, while antioxidant enzyme activities (SOD, POD, and CAT) displayed a transient increase followed by a subsequent decline. Transcriptome profiling showed marked enrichment of the protein processing in endoplasmic reticulum pathway after heat stress, suggesting activation of endoplasmic reticulum (ER) stress in pikeperch gills. With increasing stress duration, the unfolded protein response (UPR) appeared unable to re-establish ER homeostasis, shifting ire1 and atf6 toward a pro-apoptotic state. Protein-protein interaction (PPI) analysis further highlighted hub genes potentially involved in heat stress-induced ER stress and apoptosis. TUNEL staining and western blotting collectively confirmed that heat stress triggered apoptosis in pikeperch gill tissue. Overall, this study provides new insights into the physiological and molecular responses of pikeperch gills to heat stress and enhances our understanding of thermal stress adaptation in cold-water aquaculture species under climate change.

Animals↗
PubMed2006

Combined redox couples for catalytic oxidation of methane by dioxygen at low temperatures.

The combination of three redox couples Pd2+/Pd0-quinone/hydroquinone-NO2/NO creates an electron-transfer loop, which facilitates one-pot catalytic oxidation of methane selectively to methanol by dioxygen in CF3COOH at a temperature as low as 80 degrees C. This is the first example where an organic cocatalyst significantly increases the catalytic efficiency of a transition metal in the selective oxidation of methane in the presence of dioxygen.

Journal Article↗
PubMed2006

Toward monodispersed silver nanoparticles with unusual thermal stability.

A novel in situ autoreduction route has been developed, by which monodispersed silver nanoparticles with tunable sizes could be easily fabricated on silica-based materials, especially inside the channels of mesoporous silica (MPS). 13C CP/MAS NMR spectroscopy was employed to monitor the whole assembly process. It was demonstrated that the amino groups of APTS (aminopropyltriethoxyl silane)-modified MPS can be used to anchor formaldehyde to form novel reducing species (NHCH2OH), on which Ag(NH3)2NO3 could be in situ reduced. Monodispersed silver nanoparticles were thus obtained. In situ XRD and in situ TEM experiments were used to investigate and compare the thermal stabilities of silver nanoparticles on the external surface of silica gels (unconfined) and those located inside the channels of SBA-15 (confined). It was observed that unconfined silver nanoparticles tended to agglomerate at low temperatures (i.e., lower than 773 K). The aggregation of silver nanoparticles became more serious at 773 K. However, for those confined silver nanoparticles, no coarsening process was observed at 773 K, much higher than its Tammann temperature (i.e., 617 K). Only when the treating temperature was higher than 873 K could the agglomeration of those confined silver nanoparticles happen with time-varying via the Ostwald ripening process. The confinement of mesopores played a key role in improving the thermal stabilities of silver nanoparticles (stable up to 773 K without any observable coarsening), which is essential to the further investigations on their chemical (e.g., catalytic) properties.

Journal Article↗
PubMed2006

Workgroup report: public health strategies for reducing aflatoxin exposure in developing countries.

Consecutive outbreaks of acute aflatoxicosis in Kenya in 2004 and 2005 caused > 150 deaths. In response, the Centers for Disease Control and Prevention and the World Health Organization convened a workgroup of international experts and health officials in Geneva, Switzerland, in July 2005. After discussions concerning what is known about aflatoxins, the workgroup identified gaps in current knowledge about acute and chronic human health effects of aflatoxins, surveillance and food monitoring, analytic methods, and the efficacy of intervention strategies. The workgroup also identified public health strategies that could be integrated with current agricultural approaches to resolve gaps in current knowledge and ultimately reduce morbidity and mortality associated with the consumption of aflatoxin-contaminated food in the developing world. Four issues that warrant immediate attention were identified: a) quantify the human health impacts and the burden of disease due to aflatoxin exposure; b) compile an inventory, evaluate the efficacy, and disseminate results of ongoing intervention strategies; c) develop and augment the disease surveillance, food monitoring, laboratory, and public health response capacity of affected regions; and d) develop a response protocol that can be used in the event of an outbreak of acute aflatoxicosis. This report expands on the workgroup's discussions concerning aflatoxin in developing countries and summarizes the findings.

Developing Countries↗
PubMed2005

Study on conformation interconversion of 3-alkyl-4-acetyl-3,4-dihydro-2H-1,4-benzoxazines from dynamic NMR experiments and ab initio density functional calculations.

Variable-temperature NMR experiments and ab initio density functional calculations were carried out to investigate the conformation interconversion of novel chiral 3-alkyl-3,4-dihydro-2H-benzo[1,4]oxazine derivatives. With CDCl3 as the solvent, the coalescence temperatures of H2, H3, H11, and H19 of product 1 are about 289, 304, 292, and 316 K, with the corresponding activation free energies at 58.0 +/- 6.7, 60.9 +/- 7.1, 58.3 +/- 6.8, and 59.6 +/- 6.9 kJ.mol(-1), respectively. When dimethyl sulfoxide (DMSO-d6) was used as the solvent, 1H and 13C NMR signals were completely assigned at 375 K. The effects of solvent and temperature were investigated through a polarizable continuum model. At each theoretical level (MP2 or B3LYP), the changing tendencies of the calculated activation free energies and interconversion rates agree well with those of the NMR results. In addition, the interconversion rate at each specified temperature was calculated to be about 1.5 times faster in DMSO-d6 than in CDCl3. Accordingly, we failed to observe the coalescence phenomena of H3 and H19 in DMSO-d6 by NMR measurements from 296 to 375 K. The substitution effect at the R1-R5 positions was considered using density functional calculations, with the activation barriers decreasing as follows: product 6 > 3 > 1 > 7 > 2. This sequence is consistent with that of the reaction heats, except for product 7, implying that the interconversion processes may be thermodynamically controlled. Surprisingly, the substituted groups near the acetyl group in product 2 and 7 do not elevate the activation barrier but, instead, lower it somewhat, with the possible reasons for this provided in the paper.

Benzoxazines↗
PubMed2005

Separation and determination of tetrandrine and fangchinoline in herbal medicines by flow injection-micellar electrokinetic capillary chromatography with internal standard method.

A simple, rapid and precision flow injection-micellar electrokinetic capillary chromatography (FI-MEKC) system with trimethoprim as internal standard (IS) for automated quantitative analysis of tetrandrine (TET) and fangchinoline (FAN) in various herbal medicines was demonstrated. The real sample throughput was 19-40 samples per hour using the background electrolyte (BGE) containing 15mM acetic acid-15mM sodium acetate-3% (v/v) polyoxyethylene sorbitan monolaurate (Tween 20)-5% (v/v) methanol at pH 5.5. The method resulted in excellent linearity, with correlation coefficient of regression equation of 0.9996 and 0.9991 for TET and FAN, respectively. Recoveries were in the range 95-109% and 92-106% for TET and FAN, respectively.

Alkaloids↗
PubMed2005

Continuous focus tracking for real-time optical coherence tomography.

We report an approach to achieving continuous focus tracking and a depth-independent transverse resolution for real-time optical coherence tomography (OCT) imaging. Continuous real-time focus tracking is permitted by use of a lateral-priority image acquisition sequence in which the depth-scanning rate is equivalent to the imaging frame rate. Real-time OCT imaging with continuous focus tracking is performed at 1 frame/s by reciprocal translation of a rapid lateral-scanning miniature imaging probe (e.g., an endoscope). The optical path length in the reference arm is scanned synchronously to ensure that the coherence gate coincides with the imaging beam focus. The image quality improvement is experimentally demonstrated by imaging a tissue phantom embedded with polystyrene microspheres and rabbit esophageal tissues.

Animals↗
PubMed2005

[Molecular analysis of Salmonella enteritidis by pulsed-field gel electrophoresis].

OBJECTIVE: To study the relationship between different strains of Salmonella enteritidis, a molecular epidemiologic analysis method-pulsed-field gel electrophoresis was established and Salmonella enteritidis isolated from food samples were tested. METHODS: Food samples were collected from Henan province, Heilongjiang province and other provinces in 1991 - 2001. Strains were isolated and single colony of each Salmonella enteritidis strain from an agar plate was picked and enriched, then the total DNA was extracted in turn with lysozyme solution, proteinase K solution and TE buffer. The agarose pulgs were digested with restriction enzyme XbaI overnight at 37 degrees C, followed by pulsed-field gel electrophoresis (PFGE) with a CHEF Mapper system in 0.5 x TBE buffer with recirculation at 14 degrees C . DNA macrorestriction fragments were resolved on 1% agarose gels, pulse time were ramped from 5s to 45s during a 26h run at 6V/cm. A lambda ladder pulsed-field gel maker was used as a size standard. RESULTS: 30 Salmonella enteritidis strains were identified in chicken, beef, cooked meat and vegetables. 18 strains were isolated from henna province. More of the stains (22 strains) were isolated in 2001. Two distinct DNA fragment profiles, PFGE types A and B, were observed, representing 63.3% and 36.7% of the isolates respectively. Type A could be subdivided further into two subtypes. Subtype A1 represented the majority (78.9%) of type A strains and differed from subtype A2 in that the latter lacked a band in the 50kb region. There was no correlation between the strains profiles and their isolation time or region. However, all the strains isolated from the chicken were totally type A1, and showed certain epidemiological trend which can be studied in the future. CONCLUSION: The pulsed-field gel electrophoresis is a good method to study the molecular epidemiological relationship between the different Salmonella enteritidis srtains.

Bacterial Typing Techniques↗
PubMed2004

Rapid-scanning forward-imaging miniature endoscope for real-time optical coherence tomography.

We developed a miniature endoscope that is capable of rapid lateral scanning and is suitable for real-time forward-imaging optical coherence tomography (OCT). The endoscope has an outer diameter of 2.4 mm, consisting of a miniature tubular lead zirconate titanate (PZT) actuator, a single-mode fiber-optic cantilever, and a graded-index lens. Rapid lateral scanning at 2.8 kHz is achieved when the fiber-optic cantilever is resonated with the PZT actuator. This allows OCT imaging to be performed by fast lateral beam scanning followed by slow depth scanning, which is different from the conventional OCT imaging sequence. Real-time OCT imaging with the endoscope operated in the new image acquisition sequence at 6 frames/s is demonstrated.

Computer Systems↗
PubMed2004

Rapid scanning all-reflective optical delay line for real-time optical coherence tomography.

We describe a dispersion-free high-speed scanning optical delay line that is suitable for real-time optical coherence tomography, in particular, when an ultrabroadband light source is used. The delay line is based on all-reflective optics consisting of two flat and one curved mirrors. We achieve optical path-length scanning by oscillating one of the two flat mirrors with a resonant galvanometer. The delay line is compact and easy to implement. A total scanning depth of 1.50 mm with an 89% duty ratio, a maximal scanning speed of approximately 9.1 m/s, and a 4.1-kHz repetition rate has been demonstrated.

Animals↗
PubMed2004

Stepwise sliding of single actin and Myosin filaments.

Dynamics of sliding were explored in isolated actin and myosin filaments. Sliding occurs in steps. The steps are integer multiples of 2.7 nm, which is equal to the monomeric repeat along the actin filament. When filaments were forced to slide in the reverse direction, the size paradigm was the same. This size paradigm is parallel to that seen in the kinesin-microtubule system, where step size is an integer multiple of the tubulin repeat along the microtubule.

Actin Cytoskeleton↗
PubMed2004

[Fluoroquinolone resistance mutations in topoisomerase genes of Salmonella typhimurium isolates].

OBJECTIVE: Mutations in topoisomerase genes were main cause of the resistence of Salmonella typhimurium to fluoroquinolone. METHODS: The MICs of three Salmonella typhimurium isolates X2, X7, X11 to ciprofloxacin were above 32 microg/ml, 0.38 microg/ml and 0.023 microg/ml, respectively. The genetic alterations in four topoisomerase genes, gyrA, gyrB, parC, and parE were detected by multiplex PCR amplimer conformation analysis in these three strains. RESULTS: X2 isolate showed both gyrA mutations (Ser83-->Phe, Asp87-->Asn) and parC mutation (Ser80-->Arg). X7 isolate showed a single gyrA mutation (Ser83-->Phe) and X11 isolate had no changes in all of the four quinolone resistance genes, gyrA, gyrB, parC, and parE. X7 isolate with a single gyrA mutation was less resistant to ciprofloxacin than X2 with double gyrA mutations and an additional parC mutation. CONCLUSION: GyrA and parC genes play important role of the resistance of Salmonella typhimurium to ciprofloxacin.

Anti-Bacterial Agents↗
PubMed2004

[Survey and analysis on sterigmatocystin contaminated in grains in China].

In order to determine the Sterigmatocystin (ST) contaminated in grains by indirect competitive enzyme link immune sorbent assays (IC-ELISA), 1580 samples including wheat, corn and rice were taken from 12 provinces located in East-north, west-north, west-south, east and central China. Results showed that the average contaminated content of ST in wheat, corn and rice was 68.9 ug/kg, 32.2 ug/kg and 13.9 ug/kg respectively. Also, the contaminated rate was 98%, 89% and 72% respectively. The contaminated content and rate of ST was highest in wheat followed by corn and the rice ranged in third that was statistically highly significant. Severity of contamination was different in different geo-regions with higher in east China and Western China that in north-east China, central China and south-western China that were statistically highly significant.

China↗
PubMed2004

[Multiplex PCR assay against E. coli O157 in foodstuffs].

A multiplex PCR assay for detection of Escherichia coli O157:H7 was developed with 4 pairs primers which focus on its specific fliC, rfbE, SLT I and SLT II genes. The target genes fragments of the PCR assay were 560 bp, 678 bp, 210 bp and 484 bp. The multiplex PCR had very high specificity to match all the 71 tested strains including 58 E. coli strains and other 18 strains. The strain of E. coli O157:H7 was identified in one step, and the type of SLT was also identified as well. With the enrichment procedure, the strain of E. coli O157:H7 were recovered at the detection limit of 0.1 cfu/ml from artificial inoculated pasteurized milk.

Animals↗
PubMed2004

[Foodborne disease outbreaks in China from 1992 to 2001 national foodborne disease surveillance system].

OBJECTIVE: To study the foodborne disease outbreaks in the areas covered by National Foodborne Disease Surveillance System. METHODS: Total 13 provinces were included in the surveillance system, and the foodborne disease outbreaks data during 1992 to 2001 were collected. RESULTS: During 1992-2001, a total of 5770 outbreaks of foodborne disease were reported. These outbreaks caused a reported 162,995 persons to become ill. Among outbreaks for which the etiology was determined, bacterial pathogens caused the largest percentage of outbreaks (38.5%) and the largest percentage of cases (50.9%). Vibrio parahaemolyticus (31.1%) accounted for the largest number of outbreaks and cases. Chemical agents caused 37.5% of outbreaks and 28.6% of cases. CONCLUSION: More work needs to be done to improve the foodborne disease surveillance system.

China↗