动能定理在活动物体和固定物体的应用

学生对在运动的参考系中应用动能解题时,总感觉没有把握,不知如何下手,因而常常解错. 如何让学生解决活动坐标系上出现的问题呢? 首先应使学生明白,物体的速度是相对参考系而言的,参考系选取不同,物体的相对速度不同,具有的动能也不同.

Gastric stimulation for weight loss

The prevalence of obesity is growing to epidemic proportions,and there is clearly a need for minimally invasive therapies with few adverse effects that allow for sustained weight loss.Behavior and lifestyle therapy are safe treatments for obesity in the short term,but the durability of the weight loss is limited.Although promising obesity drugs are in development,the currently available drugs lack efficacy or have unacceptable side effects.Surgery leads to long-term weight loss,but it is associated with morbidity and mortality.Gastric electrical stimulation(GES) has received increasing attention as a potential tool for treating obesity and gastrointestinal dysmotility disorders.GES is a promising,minimally invasive,safe,and effective method for treating obesity.External gastric pacing is aimed at alteration of the motility of the gastrointestinal tract in a way that will alter absorption due to alteration of transit time.In addition,data from animal models and preliminary data from human trials suggest a role for the gut-brain axis in the mechanism of GES.This may involve alteration of secretion of hormones associated with hunger or satiety.Patient selection for gastric stimulation therapy seems to be an important determinant of the treatment's outcome.Here,we review the current status,potential mechanisms of action,and possible future applications of gastric stimulation for obesity.

Expansion of Small Terrestrial Mammals and Their Parasites into the Barun Valley (Makalu Mt. Region, Nepal Himalaya) Linked with Changes in Glaciation and Human Activities

The article is based on collection of small terrestrial mammals(Soriculus nigrescens,Episoriculus caudatus, Neodon sikimensis,Alticola stoliczkanus, Niviventer eha and Ochotona roylei) collected in the Barun Valley, east Nepal in the pre-monsoon period of 1973.Zoogeographic and ecological characteristics and altitudinal stratification of these species are analysed, depending both on abiotic(geomorphological and climatic) and biotic(vegetation, and human presence and activities)factors. All the captured mammals were examined for ecto- and endoparasities. Infestations of Trombiculid mites and Ixodid ticks were tightly linked to the local habitat where these ectoparasites must survive during their nonparasitic phase. Analysis of their occurrence completes the reconstruction of migration routes during the expansion of small mammals into the Barun Valley and the exacerbating influence of human activities(summer pasturing,mountaineering expeditions and trekking parties).An indicator of anthropogenic influence was the occurrence of synantropic flies. The potential medical importance of these findings is discussed.It is assumed a possible occurrence of arboviruses transmitted by ticks and also rickettsioses(transmitted by ticks and chigger mites). As far bacteriological infections, plague cannot be excluded.

Adobe After Effects内容识别填充功能初探

Adobe After Effects2019年4月新版本新增的“内容识别填充”功能,只需几步简单操作,就可以从活动视频中移除不需要的物体。本文结合实例,介绍了此功能的详细使用方法,以及使用方式不同对结果的不同影响。并对此功能的优点和目前的局限性进行分析。

GIS-based Earthquake-Triggered Landslide Hazard Zoning Using Contributing Weight Model

Earthquake-triggered landslides have aroused widespread attention because of their tremendous ability to harm people's lives and properties.The best way to avoid and mitigate their damage is to develop landslide hazard maps and make them available to the public in advance of an earthquake.Future construction can then be built according to the level of hazard and existing structures can be retrofit as necessary.During recent years various approaches have been made to develop landslide hazard maps using statistical analysis or physical models.However,these methods have limitations.This study introduces a new GIS-based approach,using the contributing weight model,to evaluate the hazard of seismically-induced landslides.In this study,the city and surrounding area of Dujiangyan was selected as the research area because of its moderate-high seismic activity.The parameters incorporated into the model that related to the probability of landslide occurrence were:slope gradient,slope aspect,geomorphology,lithology,base level,surface roughness,earthquake intensity,fault proximity,drainage proximity,and road proximity.The parameters were converted into raster data format with a resolution of 25×25m2 pixels.Analysis of the GIS correlations shows that the highest earthquake-induced landslide hazard areas are mainly in the hills and in some of the moderately steep mountainous areas of central Dujiangyan.The highest hazard zone covers an area of 11.1% of the study area,and the density distribution of seismically-induced landslides was 3.025/km2 from the 2008 Wenchuan earthquake.The moderately hazardous areas are mainly distributed within the moderately steep mountainous regions of the northern and southeastern parts of the study area and the hills of the northeastern part;covering 32.0% of the study area and with a density distribution of 2.123/km2 resulting from the Wenchuan earthquake.The lowest hazard areas are mainly distributed in the topographically flat plain in the northeastern part and some of the relatively gently slopes in the moderately steep mountainous areas of the northern part of Dujiangyan and the surrounding area.The lowest hazard areas cover 56.9% of the study area and exhibited landslide densities of 0.941/km2 and less from the Wenchuan earthquake.The quality of the hazard map was validated using a comparison with the distribution of landslides that were cataloged as occurring from the Wenchuan earthquake.43.1% of the study area consists of high and moderate hazardous zones,and these regions include 83.5% of landslides caused by the Wenchuan earthquake.The successful analysis shows that the contributing weight model can be effective for earthquake-triggered landslide hazard appraisal.The model's results can provide the basis for risk management and regional planning is.

Comparative studies on storage cells in tardigrades during starvation and anhydrobiosis

The impact of starvation and anhydrobiosis on the number and size of the storage cells in the tardigrade species Milnesium tardigradum, Paramacrobiotus tonollii and Macrobiotus sapiens was investigated to gain more insight on the energetic side of anhydrobiosis. Storage cells are free floating cells within the body cavity of tardigrades and are presumed to store and release energy in form of glycogen, protein and fat to maintain a constant nutrient regime for the other tissues. The body size of the animals was not correlated with the size of the storage cells, however, M. tardigradum the largest species analysed also had the largest storage cells. A reduction in the size of the storage cells is apparent in all three species after seven days of starvation. A seven-day period of anhydrobiosis leads to a decrease in cell size in M. tardigradum but not in P. tonollii and M. sapiens. Although M. sapiens was raised on green algae, and M. tardigradum and P. tonollii were fed with rotifers and nematodes this difference in nourishment was not reflected in the response of the storage cells to anhydrobiosis

Ontogenetic changes in feeding and food preferences of the dog conch Laevistrombus canarium Linnaeus 1758 (Mollusca： Gastropoda) from Merambong shoal, Malaysia

Laevistrombus canarium is one of the marine gastropod mollusks that have high commercial value, particularly in the aquaculture sector in Malaysia. This study was conducted to determine the feeding and food items of L. canarium at different ontogenetic stages （juveniles, sub-adults and adults） from Merambong shoals, Malaysia. Field observations on feeding activity were conducted, followed by detailed laboratory analysis on the stomach content. Five-minutes observations on randomly selected individuals were conducted at the field sampling site and their feeding activities were recorded with reference to age stage. Various shell sizes from each ontogenetic stage were randomly collected and quickly anaesthetized with ice and preserved in 10% formalin before being transported to the laboratory for stomach content analyses. Field observations showed that L. canarium mainly grazed on epiphytes occurring on seagrass （46.67%）, followed by sediment surface （40%） and epiphytes occurring on macroalgae （13.33%）. Stomach content analyses showed a significant difference （P〈0.05） in gastro-somatic index （Gasi） between the juveniles （0.39±0.05）, sub-adults （0.68±0.09） and adults （0.70±0.05） （P〈0.05）. Food items found in the conch stomach include diatoms, detritus, foraminifera, seagrass and macroalgae fragments, sand particles and shell fragments. The Index of Relative Importance （%IRI） indicates three main types of food dominated the three ontogenetic stages namely diatoms, sand particles and detritus. However, no significant difference （P〉0.05） was detected between the three main food items （diatoms, sand particles and detritus） among the ontogenetic stages. Therefore, feeding activity revealed the role of the dog conch in the marine food network. While, classification of the types of food consumed by L. canarium through stomach content analysis determines the particular position of the gastropod in the food chain. Further studies are needed to provide a better insight between trophic relationships ofL. eanarium with marine ecosystem.

Toxic Effects of Seed Methanolic Extracts of Endemic Albizia Species （Fabaceae） from Madagascar on Animals

In order to find natural compounds of interest such as pesticides and therapeutic molecules, toxicological properties of seed methanolic extracts （SME） of nine Malagasy Albizia species were investigated. Toxicity was assessed on living animals by intraperitoneal and oral route, and pharmacological effects on isolated organs. All SME induced various disorders in mice but the signs of the nervous system disturbs were the earliest and the most often observed. The main organ lesions, examined on histological sections, induced vasodilatation, inflammatory infiltrate of neutrophil polymorphonuclears and hemorrhagic areas. At low concentrations （until 20 p.g/mL）, A. masikororum and A. viridis provoked on isolated auricular a positive inotrope effect followed by a progressive inhibition of the contraction and a complete atrial arrhythmia. Besides, A. viridis and A. bernieri induced some hepatic functional impairment after a chronic treatment during one month. Albizia greveana with a LD50 of 1.13-2 mg/kg was the most toxic and Albizia bernieri the least one with a LD50 of 52 mg/kg. Alkaloids and/or saponins, the major chemical groups found by phytochemical screening on these extracts, could be responsible of their toxicity.

Expression and immunoactivity of chimeric particulate antigens of receptor binding site-core antigen of hepatitis B virus

AIM: To improve the immunogenicity of receptor binding site of hepatitis B virus (HBV) on preS1 antigen using HBV core antigen as an immuno-carrier. METHODS: One to 6 tandem copies of HBV preS1 (21-47) fragment were inserted into HBcAg at the sites of aa 78 and 82, and expressed in E.coli. ELISA, Western blot and animal immunization were used to analyze the antigenicity and immmunogenicity of purified particulate antigens. The ability to capture HBV by antibodies elicited by chimeric particles was detected with immuno-capture PCR. RESULTS: Recombinant antigens CI, CII, CIII carrying 1-3 copies of HBV preSl (21-47) individually could form virus-like particles (VLPs), similar to HBcAg in morphology. But recombinant antigens carrying 4-6 copies of HBV preSl (21-47) were poorly expressed in E.coli. Chimeric antigens were lacking of immunoreactivity with anti-HBc monoclonal antibodies (McAbs), but still reserved good immunoreactivity with anti-HBe McAbs. CI, CII, CIII could strongly react with anti-preS1 McAb, suggesting that preS1 (21-47) fragment was well exposed on the surface of chimeric VLPs. Three chimeric VLP antigens (CI, CII and CIII) could stimulate mice to produce high-level antibody responses, and their immunogenicity was stronger than non-particulate antigen 21-47*6, containing 6 copies of preS1 (21-47). Mouse antibodies to CI, CII and CIII were able to capture HBV virions in immuno-capture PCR assay in vitro. CONCLUSION: Chimeric particulate antigens of receptor binding site-core antigen of HBV can elicit strong antibody responses to preS1. They have a potential to be developed into prophylactic or therapeutic vaccines against HBV infection.

ANTITUMOR ACTIVITY OF IMMUNOCONJUGATES COMPOSED OF BOANMYCIN AND MONOCLONAL ANTIBODY

Boanmycin (bleomycin A6 . BM) . an antitumor antibiotic, was conjugated to monoclonal antibodies including R19, H 111 and CCT2. The immunoconjugates exhibited selective cytotoxicity to related target cells including cecum cancer Hce-8693 cells, liver cancer BEL-7402 cells and leukemia CEM cells. They were highly effective against related human tumor xenografts in nude mice, and the inhibition rates by the conjugates were much higher than those by free BM. The inhibition rate by R19-BM conjugate against human cecum cancer xenografts reached 90%. BY immunoelectron microscopy, CCT2-BM conjugate showed specific binding and internalization in leukemia CEM cells. The results indicate that boanmycin-monoclonal antibody immunoconjugates are highly active both in vitro and in vivo.

Climate Change and Environmental Impact Caused by Anthropogenic

For the last two decades the world has undergone a population explosion which has been accompanied by a speeding up of urbanization and land use for industrial and agricultural products. These involve a vast increase in the discharge of pollutants into very different receiving water bodies, and have had adverse effects on the various components of the environment. For a long time, human has concerned a little of the natural environment. It is obvious that this variation in surface temperature of the earth increases the level of sea due to snowmelt. So climate change is manifested by many phenomena： floods, droughts, fires, tornadoes, cyclones, earthquakes, volcanic eruptions, diseases etc.. The statement today is dramatic. Entire regions were devastated and many rivers and lakes have become polluted around the world. Pollution has it nature which is hard to be absorbed. Where did the different pollutants come from？ What are the risks to the aquatic environment？ To prevent and combat the general decline of these ecosystems, it is important to distinguish and determine the effects of different sources of pollution and any changes that may suffer the physical environment. The climate depends primarily on changes in earth orbit parameters, which affect the solar radiation received by the earth surface. Therefore, human participates strongly to these changes, for example, pollution is the main reason to argue the greenhouse effect, an increase of anthropogenic carbon dioxide （CO2） into the atmosphere, which promotes global warming to the planet. These modifications are already applied in order to ensure durable development in water resources by controlling discharges into streams to preserve water resources for future generations and to ensure reconciliation between man-climate and environment.

Exercise and antioxidant supplements in the elderly

Both exercise and aging increase reactive oxygen species （ROS）, which can result in damage to cells. Aging is the result of damage caused by ROS to the mitochondrial genome in post mitotic cells and numerous studies have demonstrated an increase in ROS or their byproducts with exercise. ROS can cause oxidative stress as they overwhelm the antioxidant cellular defenses. Therefore interventions aimed at limiting or inhibiting ROS production, such as supplementation with antioxidant vitamins, should be able to reduce fatigue during muscle contraction and the rate of formation of aging changes with a consequent reduction of the aging rate and disease pathogenesis. However, it has been shown that ROS are essential signaling molecules which are required to promote the health benefits of exercise and longevity. In young individuals, ROS are required for normal force production in skeletal muscle, for the development of training-induced adaptations in endurance performance, as well as for the induction of the endogenous defense systems. Thus, taking antioxidants during training, in young athletes, seems to be detrimental. However, antioxidant supplementation may be expected to be beneficial and is receiving growing attention in the active old population. In this manuscript we review the literature associated with the main areas of interest in this topic.

Changes in Global DNA Methylation Intensity and DNMT1 Transcription During the Aging Process of Scallop Chlamys farreri

DNA methylation is an important epigenetic regulatory mechanism that influences genomic stability, gene activation, X-chromosome inactivation and other factors. A change in DNA methylation is usually associated with aging and cellular senescence. DNA methyltransferase 1(DNMT1) is the most abundant DNA methyltransferase, and it plays an important role in maintaining the established methylation pattern during DNA replication in vertebrates. Although the effect of aging on DNA methylation has been well studied in vertebrates, little research has been conducted in invertebrates, especially in marine bivalves. In this study, we examined global DNA methylation levels in four groups of adult Zhikong scallop Chlamys farreri at different ages. The results showed that both the age and tissue type had a strong effect on the DNA methylation. In addition, a significant decrease in DNA methylation with aging(1–4 years) can be detected in mantle, kidney and hepatopancreas. We further measured the change in DNMT1 transcript abundance using quantitative reverse transcription PCR(q RT-PCR), which revealed that DNMT1 transcription significantly decreased with aging in mantle and hepatopancreas and strongly correlated with DNA methylation(R = 0.72). Our data provided greater insight into the aging-related decline of DNA methylation, which could aid in gaining a better understanding of the relationship between DNA methylation and the aging process in bivalve mollusks.

母婴连体

"人是早产三年的动物,因此人出生后的这三年极为重要。尽管人的生物体脱离了母体,但是它实际上同母体仍然没有分开,仍然有一个未分化期。"由于人是早产三年的动物,因此人出生后的这三年极为重要。尽管人的生物体脱离了母体,但是它实际上同母体仍然没有分开,仍然有一个未分化期。母亲和婴儿仍是一体的,仿佛是一对连体婴儿那样.母婴的关系仍然是孕妇同胎儿的关系,不过就像试管婴儿那样,生长环境从宫里转移到宫外而已。

How to Make a Submarine Disappear

雷达可以通过声波探测出某一范围内所有的活动物体,而对潜水艇来说,如何逃过雷达的追踪就变得尤为重要。日前科学家们开发出一种新技术,能通过改变声波的传送路径使之遁于无形,或者绕过声波探测器。如果这一研究成功,将能在军事和民用领域带来意想不到的变化。

A Middle Triassic stem-neopterygian fish from China shows remarkable secondary sexual characteristics

Secondary sexual characteristics are features that appear at sexual maturity and distinguish the two sexes of a species. They are readily observed and studied in living animals, but the phenomenon is rather more difficult to identify in fossil taxa. Here we report a new sexually dimorphic stem-neopterygian fish, Venusichthys comptus gen. et sp. nov., based on 30 exceptionally well-preserved specimens from the Middle Triassic （Pelsonian, Anisian） Luoping Lagerst^itte of eastern Yunnan, China. The discovery represents the oldest known secondary sexual characteristics in Neopterygii. These characteristics, including pointed tubercles on cranial bones, scales and fins, and hook-like contact organ anterior to the anal fin, have three inferred primary functions： maintenance of body contact between the sexes during prespawning behavior or spawning; stimulation of the females during breeding; and defense of nests and territories. Lacking a specialized anal fin in the presumed males, Venusichthys would likely have a different reproductive strategy from peltopleurids and other potentially viviparous stem-neopterygians. Moreover, Venusichthys shows a unique character combination distinguished from any other stem-neopterygian families and consequently represents a new family of this clade. Assuch, the new finding provides an important addition for understanding the behavior, reproduction, and early diversification of Neopterygii.

Origin of new genes after zygotic genome activation in vertebrate

New genes are drivers of evolutionary innovation and phenotypic evolution. Expression of new genes in early development raises the possibility that new genes could originate and be recruited for functions in embryonic development, but this remains undocu- mented. Here, based on temporal gene expression at different developmental stages in Xenopus tropicolis, we found that young protein-coding genes were significantly enriched for expression in developmental stages occurring after the midblastula trans- ition （MBT）, and displayed a decreasing trend in abundance in the subsequent stages after MBT. To complement the finding, we demonstrate essential functional attributes of a young orphan gene, named as Fog2, in morphological development. Our data indicate that new genes could originate after MBT and be recruited for functions in embryonic development, and thus provide insights for better understanding of the origin, evolution, and function of new genes.

New advances in biomimetic surface

Anti-adhesion is a common phenomenon in living organisms, which is the evolution results to adapt their living surroundings. From the perspective of surface type, there are two typical anti-adhesion mechanisms： micro- and nano- surface structures and liquid-covered surface. Many living organisms possess one or two of these anti-adhesion surfac- es in order to achieve superior anti-adhesion, for example, soil animals like mole cricket and earthworm [1]. Carnivo- rous pitcher plant Nepenthes can capture and digest insects to meet the fundamental nutrients needs. When the insects crawl on its slippery peristome, they could easy-sliding into the picher, known as ＂aquaplaning＂. Wong et al. [2] at Harvard University has designed and fabricated slippery surface mimicking this slippery mechanism in Nepenthes, the results of which was published in Nature. However, questions remain about the mechanism underlying its func- tion, especially for the liquid film formation mechanism.

Comparative Study on the Dielectric Properties Between Living and Non-living from Human and Animal Livers

The data of d ieleclric properties of hum an tissues m ably com es from an in al tissues or hum an corpse at present U p to now, there has not been a report of dielectric properties of human living liver. This paper aims to studying the dielectric properties of hum an living liver and corn paring the results with those of an in al living liver as well as the human non-livhg liver. In vitro measurements of living and non-living livers from human and rabbitare shown in the range of 10 Hz to 100 MHz. Analysis of the conductivity, perm ittivity and characteristic param eters from the data were made. The conductivity of three kinds of liver were markedly different at low frequency： 0.06 S/m （living rabbit liver）, 0.13 S/m （living hum an liver） and 0.24 S/m （non-living hum an liver）; The Cole param eters that best characterize the liver of hum an and rabbit are RO, fc1,△R I and R ∞ ;The Cole param eters that best characterize the living and non-living liver ofhum an are RO, fc1,△R I,△R2 and R ∞. In conclusion,we can＇t substitute the dielectric properties of anin al or hum an corpse liver for the living human liver. The results suggest that the study on the dielectric properties of living hum an tissues has great sign ificance.

Collective motion of bacteria and their dynamic assembly behavior

In recent years, active matter systems have attracted considerable attentions due to their complex dynamic behaviors in physical and material science. In particular, microorganism systems have served as model systems for observing dynamic assembly and collective motility of active particles and significant progresses have been made on in-depth understanding of how high density bacteria colony behaves in the non-equilibrium state. In this mini-review, we mainly focus on the collective motion of bacteria and their dynamic assembly from four aspects： （1） the general phenomenon and biological mechanism of bacterial collective motion; （2） the common experimental techniques for studying bacterial motility; （3） some active systems on exploring bacterial collective behavior, which include both non-restricted free suspensions and those in relative confined geometric space; （4） the phenomenological and descriptive statistical methods and physical models on the underlying laws that lead to large-scale coordinate patterns in multicellular systems. This review aims to give a general picture of the collective motion in bacterial active matter systems experimentally and theoretically in order to reflect the interplays between individuals among populations in motion. It is expected that the general regulation rules related to the boundary effects in the complex systems and materials can be elucidated to some extent.