A calculation approach for current density distribution evolution of secondary electrons using differential algebra method.

In this study, the concept of the current density distribution (CDD) evolution of secondary electron (SE) beam is presented, and a novel approach using the differential algebra (DA) method is proposed to calculate the CDD evolution of the SE beam. Firstly, the emitted SE beam is divided into some beamlets in polar and azimuth angle directions. For each beamlet only one reference trajectory is traced using DA method. As a result, the transfer properties for this beamlet are obtained. Using the transfer properties, the current density function at arbitrary plane for the beamlet can be derived, in which the initial angle distribution, energy distribution and emission source size are considered. And then, the current density function is integrated, resulting in the CDD of this beamlet at arbitrary plane. Finally, the CDD evolution of the whole SE beam is obtained by superposing the CDDs of all beamlets. As an example, a SE detection system for a scanning electron microscope (SEM) is calculated using the proposed approach and therefore the SE CDD evolution is obtained and analyzed. Furthermore, experiments for observing the SE image of detector are performed, and the calculated SE CDD and the corresponding simulation images well explained the experimental results, validating the proposed calculation method. The proposed approach can be potentially applied for optimizing the SE detection system and therefore improving the collection efficiency of SE.

Antioxidant mechanism of a continuous microenvironment regulation system for prolonging the shelf-life of red grapes.

Red grapes (Vitis vinifera L.) have a high sugar content, thin skins, and relatively short shelf-life after harvesting. We developed polylactic acid/polybutylene succinate film, prepared by extrusion of polylactic acid and polybutylene succinate, that significantly prolonged the shelf-life of red grapes from 8 to 12 days by delaying the loss of weight, loss of hardness, and reduction in soluble solid content after harvesting. Further mechanistic study showed that this modified atmosphere film delayed the senescence of harvested red grape, the phenomenon that was highly related to the lower active oxygen species production and higher antioxidant enzyme activity compared to the non-packaged grape. The proposed continuous and dynamic microenvironment regulation system is a promising method to study the mechanisms of respiratory metabolism in fruit and extends food shelf-life while reducing food waste. PRACTICAL APPLICATION: In this study, we designed a means to microenvironmental regulatory packaging that directly creates a continuous, dynamic, and monitorable microenvironment. To ensure that the fruit inside the package underwent coordinated aerobic and anaerobic respiration, we melt-extruded polylactic acid (PLA) and polybutylene succinate (PBS) to form a homogeneous biodegradable film. We demonstrated that the best preservation results were achieved with a film comprising an 80/20 PLA-to-PBS ratio. This film can prolong the shelf-life of fruits by regulating respiratory metabolism.

Application of functionalized chitosan in food: A review.

Environmental and sustainability issues have received increasing attention in recent years. As a natural biopolymer, chitosan has been developed as a sustainable alternative to traditional chemicals such as food preservation, food processing, food packaging, and food additives due to its abundant functional groups and excellent biological functions. This review analyzes and summarizes the unique properties of chitosan, with a particular focus on the mechanism of action for its antibacterial and antioxidant properties. This provides a lot of information for the preparation and application of chitosan-based antibacterial and antioxidant composites. In addition, chitosan is modified by physical, chemical and biological modifications to obtain a variety of functionalized chitosan-based materials. The modification not only improves the physicochemical properties of chitosan, but also enables it to have different functions and effects, showing promising applications in multifunctional fields such as food processing, food packaging, and food ingredients. In the current review, applications, challenges, and future perspectives of functionalized chitosan in food will be discussed.

Oseltamivir Treatment for Influenza During the Flu Season of 2018-2019: A Longitudinal Study.

Background: Oseltamivir resistance in influenza virus (IFV) has been of widespread concern. An increase in the frequency of viruses with reduced inhibition was observed. Whether oseltamivir is effective is uncertain. We conducted this study to understand the real-world situation in northern China and the clinical efficacy for patients with IFV infection after the use of oseltamivir. Methods: The longitudinal study was performed on influenza-like illness (ILI) cases in a tertiary general hospital in Beijing, China during the flu season of 2018-2019. All ILI cases (≥18 years) were recruited into the study. We analyzed the effect of the oseltamivir therapy on the number of clinic visits, hospitalization frequency, and the duration of fever and cough. Results: A total of 689 ILI patients were recruited in this study with 355 in the oseltamivir therapy group and 334 in the supportive therapy group. Among the ILI patients, 388 patients were detected for IFV infection (364 IFV-A and 24 IFV-B) and divided into two groups with or without the oseltamivir therapy (302 vs. 86). There were no significant differences in the basic characteristics between the oseltamivir and supportive therapy groups in the ILI patients or in the IFV positive patients (all p < 0.05). After adjusting for the potential confounders, oseltamivir therapy reduced the times of clinic visits in the ILI and IFV positive patients (p = 0.043 and p = 0.011). No effectiveness with oseltamivir therapy was observed in the outcomes of hospitalization frequency, and the duration of fever and cough. Conclusion: Oseltamivir use may reduce the times of clinic visits. However, we did not observe the differences in the duration of fever, cough, and the frequency of hospitalization between oseltamivir therapy and supportive therapy.

Controlled moisture permeability of thermoplastic starch/polylactic acid/poly butylene adipate-co-terephthalate film for the autolysis of straw mushroom Volvariella volvacea.

Straw mushrooms are prone to autolyze, leading to a high requirement of environmental humidity. In this work, thermoplastic starch/polylactic acid/poly (butylene adipate-co-terephthalate) (TPS/PLA/PBAT) film was produced by extrusion. The moisture permeability of the film was controlled by adjusting the content of TPS, which could be expected to further control humidity of the microenvironment in the package. Results revealed that the water vapor transmission rate of the film linearly increased from 612.31 g/m2·24 h to 1082.50 g/m2·24 h with the increase in the TPS concentration. The TPS/PLA/PBAT film with 30 wt% TPS showed the strongest inhibition on the autolysis of straw mushrooms compared with other groups, effectively delaying the increase in the free water, soluble solid content, rate of weight loss, and polyphenol oxidase of straw mushrooms and extending the shelf life of straw mushrooms from 24 h to 72 h.

Leucandioxoles A and B, two 1,3-benzodioxole derivatives from the South China Sea sponge Leucandra sp.

Two new 1,3-benzodioxole derivatives, leucandioxoles A and B (1-2), together with two known related compounds (3-4), have been isolated from the South China Sea sponge Leucandra sp. The structures of all compounds were clearly elucidated on the basis of spectroscopic analyses and compared with the literatures. The cytotoxicity against A549, Hep G2, MDA-MB-231, and HeLa cell lines of 1-4 were evaluated. Only compound 1 exhibited moderate activity against MDA-MB-231 cells with the IC50 value of 7.98 ± 0.74 µM.

Characterization of PLA-P3,4HB active film incorporated with essential oil: Application in peach preservation.

This study aimed to develop an active film by using biodegradable materials and antioxidant essential oils to improve gas and water vapor permeability during peach preservation. O2 and CO2 volume fractions and water status were investigated by using an oxygen meter and conducting low-field nuclear magnetic resonance (LF-NMR), respectively. Results revealed that the film added with angelica essential oil (AEO) had a 49.4% increase in 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity and high O2 and CO2 transmission rates and water vapor permeability. The film added with AEO showed the best preservation effect, effectively delaying the oxidation of peach, maintained the combined water, and extended the shelf life of peaches to more than 15 days. This study provided a relatively new LF-NMR method for tracking the internal water status of packaged peaches and served as an effective reference for the development of active food packaging.

High order aberrations calculations of Wien filters using differential algebra methods.

In this paper, a novel scheme based on the differential algebraic (DA) method is proposed to analyze the electron optics properties of the Wien filters. A new software package is then developed, to compute the geometrical and chromatic aberrations up to the fifth order of the Wien filters. For examples, the aberrations of single filter and the double filters are calculated. The calculated geometrical aberration coefficients are comparable with the counterpart calculated by Tang's theory. However, both theories can only match with each other in the calculation of the chromatic aberration coefficient when the dispersion ray is taken into consideration in Tang's theory.

High order aberration calculations of a quadrupole-octupole corrector using a differential algebra method.

A Differential algebraic method is of an effective technique in computer numerical analysis. It implements conveniently differentiation up to arbitrary high order, based on the nonstandard analysis. In this paper, the differential algebra (DA) method has been employed to compute the high order aberrations up to the fifth order of electron lenses with quadrupole and octupole corrector whose electric/magnetic fields are in the forms of discrete arrays, for example, the files computed by FEM or FDM method. The quadrupole and octupole electro-magnetic fields of arbitrary point are obtained by local analytic expressions, and then field potentials are transformed into new forms which can be operated in the DA calculation. The program has been developed and tested as well. The geometric and chromatic aberrations coefficients up to fifth order of electron lenses with quadrupole and octupole corrector are calculated by the developed program.

Three New Cytotoxic Polyhydroxysteroidal Glycosides from Starfish Craspidaster hesperus.

Three new polyhydroxysteroidal glycosides, hesperuside A (1), B (2), and C (3), as well as a known novaeguinoside A (4), were isolated from the ethanol extract of starfish Craspidaster hesperus collected from the South China Sea. Their structures were elucidated by extensive spectroscopic methods and chemical evidence. The compounds 1-3 present unprecedented carbohydrate chain 3-O-methyl-ß-d-galactopyranose, which differ from each other in the side chains. These compounds exhibited cytotoxicity against human tumor cells BEL-7402, MOLT-4, and A-549 in vitro.

Three new aaptamine derivatives from the South China Sea sponge Aaptos aaptos.

Three new aaptamine derivatives (1-3), together with six known related compounds (4-9), have been isolated from the South China Sea sponge Aaptos aaptos. The structures of all compounds were unambiguously elucidated on the basis of spectroscopic analyses. Compounds 1, 4, 5, 7, and 9 showed cytotoxic activities against HeLa, K562, MCF-7, and U937 cell lines with IC50 values in the range of 0.90-12.32 µM.

[Simultaneous analysis of 4 non-steroidal anti-inflammatory drug residues in mutton muscle using high performance liquid chromatography assisted by ultrasonic-microwave extraction].

A method for the simultaneous determination of 4 non-steroidal anti-inflammatory drug (NSAID) residues, including flunixin meglumine, meloxicam, diclofenac sodium and ketoprofen, in mutton muscle was developed using high performance liquid chromatography assisted by ultrasonic-microwave extraction. The NSAIDs were extracted with acidified ethanol and purified by a diatomite column. The subsequent analysis of NSAIDs was achieved on a Hypersil C18 column (250 mm x 4.6 mm, 5 microm) with the mobile phase of acetonitrile-0.2% triethylamine (40 : 60, v/v, pH 3.5 adjusted by phosphoric acid) at a flow rate of 0.8 mL/min at 30 degrees C. The detection wavelength was set at 255 nm. The 4 NSAIDs were well separated within 20 min. The correlation coefficients for 4 NSAIDs were from 0.999 3 to 0.999 8 with the limits of detection (LOD, S/N = 3) of 5-10 microg/kg and the limits of quantification (LOQ, S/N = 10) of 15-30 microg/kg. The recoveries were in the range of 65.3% - 99.6% with the relative standard deviations (RSDs) less than 15%. This method is simple, rapid and highly sensitive, and can meet the requirement for the qualitative and quantitative analysis.

[Epidemiology of bacterial dysentery diagnosed clinically in Beijing: analysis of 652 patients].

OBJECTIVE: To investigate the epidemiological and clinical characteristics of acute bacterial dysentery in recent years in Beijing so as to provide scientific reference for prevention and control of enteric infectious diseases. METHODS: The data of age, occupation, symptoms, signs, pathogen detection of 652 patients with acute bacterial dysentery diagnosed clinically from April 2007 to October 2007 were analyzed retrospectively. RESULTS: The occupations of the 652 patients included office workers and functionaries (31.4%), students (29.4%), retirees (9.8%), unemployed and housewives (7.1%), commercial attendants (6.3), workers (4.8%), teachers (4.1%), and others (7.1%). Diarrhea, stomach ache, and fever were the main symptoms. Tenesmus and tenderness of left lower quadrant abdomen were infrequent. The positive rate of fecal bacterial culture was 17.7%. 8.9% of the patients were diagnosed as with bacterial dysentery by fecal bacterial culture. CONCLUSION: Most of the patients with bacterial dysentery in Beijing are young adults. The positive rate of fecal bacterial culture is low. It is difficult to differentiate bacterial dysentery from other diarrheal diseases.

Highly enantioselective phenylacetylene addition to aromatic ketones catalyzed by cinchona alkaloid-aluminum complexes.

The catalytic asymmetric addition of phenylacetylene to aromatic ketones is reported. The catalyst, generated from commercially available Cinchona alkaloids and industrially available triethylaluminum, gives the expected tertiary alcohols with good enantiomeric excess (70-89%) and yields (60-83%). No previous case has been reported successfully using triethylaluminum as a Lewis acid in the asymmetric alkynylation of carbonylic derivatives, and thus we provide a new method to obtain optically active tertiary propargyl alcohols.

Highly enantioselective phenylacetylene additions to ketones catalyzed by (S)-BINOL-Ti complex.

The readily available and inexpensive (S)-BINOL ligand in combination with Ti(O(i)Pr)(4) is an effective chiral catalyst for the catalytic asymmetric addition of alkynylzinc to unactivated simple ketones. Good to excellent enantioselectivities were achieved. No previous case has been reported successfully using BINOL to catalyze the addition of phenylacetylene to unactivated ketones, and thus the utility of BINOL in asymmetric catalysis is expanded.