On the Vortex Sheets of Compressible Flows

This paper provides a review of the recent results on the stability of vortex sheets in compressible flows.Vortex sheets are contact discontinuities of the underlying flows.The vortex sheet problem is a free boundary problem with a characteristic boundary and is challenging in analysis.The formulation of the vortex sheet problem will be introduced.The linear stability and nonlinear stability for both the two-dimensional two-phase compressible flows and the two-dimensional elastic flows are summarized.The linear stability of vortex sheets for the three-dimensional elastic flows is also presented.The difficulties of the vortex sheet problems and the ideas of proofs are discussed.

“十四五”时期我国财政运行的宏观经济环境及基本定位

基于对经济总量、增速、居民收入、消费、就业及民生保障等方面发展基础的分析,结合“十四五”及今后一段时期我国经济发展面临的国内外环境、发展动能切换、结构调整等因素,对财政运行的宏观环境做出研判。从社会主要矛盾具有持续性、人口老龄化问题、财政收支缺口以及发展新动能显现效果具有等待期等角度,分析财政运行面临的核心挑战。有效应对这些挑战的路径在于加快建立现代财政制度。应当坚持财政作为国家治理的基础和重要支柱这一总体定位,坚守为推动实现现代化强国目标提供战略性支撑,以扩大有效内需为基点助推我国在短期内迈入高收入经济体。同时要大力推进财政本身的制度建设,确保运转顺畅和可持续,并为推动完善宏观经济治理提供桥梁。

A novel rock bolting system exploiting steel particles

The effectiveness of rock bolting in ground control has been extensively investigated,mainly for resin based systems.Alternative coupling materials are needed to have good mechanical performance and to reduce the economic impact.This study proposed a new bolting system exploiting steel particles as coupling material.The applicability of this system was assessed by laboratory and field pullout tests,assisted by digital imaging correlation(DIC),infrared thermography(IRT)and acoustic emission(AE).The results indicated that,for a 20 mm diameter bolt,the suitable steel particle size and corresponding inner diameter of borehole were 1.4 and 28 mm,respectively.For bolts installed in steel tubes,the particles improved the loading capacity compared to the resin bonded ones.Additional pullout tests on cement blocks indicated that steel particles can be effective for hard rock,whilst resin was a better choice for bolting of soft rock.Similar understanding was obtained by pullout tests in engineering fields,which demonstrated that the steel particles coupled bolts can provide favorable effects in hard rock mass,while the effects were negligible when installed in extremely soft coal mass.The wide set of multi-technique measurements helped to understand the mechanisms involved in the performance of the bolting system with coupling steel particles.

Incorporation ofγ-aminobutyric acid and cesium cations to formamidinium lead halide perovskites for highly efficient solar cells

The stability issue has become one of the main challenges for the commercialization of perovskite solar cells(PSCs).Formamidinium(FA)-based perovskites have shown great promise owing to their improved thermal and moisture stability.However,these perovskites are suffering from phase transition and separation.Here,a method of incorporating of γ-aminobutyric acid(GABA) and cesium cations into FAPbl_(3) is developed to improve the phase stability.It is demonstrated that the crystallinity of α-FAPbl_(3) phase is greatly improved and the phase transition temperature is significantly dropped.The resultant solar cell therefore obtains a champion power conversion efficiency(PCE) of 23.71%,which is one of the highest efficiencies for methylammonium-free PSCs.Furthermore,it shows an impressively enhanced stability under illumination,exhibiting the great potential of FA-based perovskites for efficient and stable solar cells.

FORMATION OF SINGULARITY FOR COMPRESSIBLE VISCOELASTICITY

The formation of singularity and breakdown of classical solutions to the three- dimensional compressible viscoelasticity and inviscid elasticity are considered. For the compressible inviscid elastic fluids, the finite-time formation of singularity in classical solu- tions is proved for certain initial data. For the compressible viscoelastic fluids, a criterion in term of the temporal integral of the velocity gradient is obtained for the breakdown of smooth solutions.

Simulation of the gravitational wave frequency distribution of neutron star-black hole mergers

LIGO-Virgo has observed the gravitational waves(GWs)from the coalescence of binary black hole(BBH)and binary neutron star(BNS)during O1 and O2,and the ones from NS-BH are expected to be hunted in the operating O3 run.The population properties and mass distribution of NS-BH mergers are poorly understood now,thus researchers simulated their chirp mass(M)distribution by a synthetic model,in which the BHs and NSs were inferred by LIGO-Virgo(O1/O2),and obtained the values in the range of 2.1 M_(⊙)<M<7.3 M_(⊙).In this paper,we further simulate the GW frequency(fGW)distribution of NS-BH mergers by the above-stated synthetic model,with a basic binary system model through the Monte Carlo method.Our results predict that the median with 90%credible intervals is 165+475-64 Hz in the case of Schwarzschild BH when the system just before merger,and this GW frequency is expected to increase several times in the merger stage,which is lying in the frequency band of LIGO-Virgo,i.e.,about 15 Hz to a few kHz.Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.

On the inviscid limit of the compressible Navier-Stokes equations near Onsager's regularity in bounded domains

The viscous dissipation limit of weak solutions is considered for the Navier-Stokes equations of compressible isentropic flows confined in a bounded domain.We establish a Kato-type criterion for the validity of the inviscid limit for the weak solutions of the Navier-Stokes equations in a function space with the regularity index close to Onsager’s critical threshold.In particular,we prove that under such a regularity assumption,if the viscous energy dissipation rate vanishes in a boundary layer of thickness in the order of the viscosity,then the weak solutions of the Navier-Stokes equations converge to a weak admissible solution of the Euler equations.Our approach is based on the commutator estimates and a subtle foliation technique near the boundary of the domain.

Tsen-Hwang Shaw: Founder of Vertebrate Zoology in China

“The founder of vertebrate zoology in China;an erudite scholar of insect,fish,bird and mammal research;combining taxonomy and animal ecology,and pioneering in biostatistics.”These are memorial comments written by Chinese mammalogist Wuping Xia on the 15th anniversary of the death of Professor Tsen-Hwang Shaw(寿振黄,1899-1964),which offers an overview of the academic contributions of Professor Shaw(Fig.1).

Application of different fiber structures and arrangements by electrospinning in triboelectric nanogenerators

In recent years,nanogenerators(NGs)have attracted wide attention in the energy field,among which triboelectric nanogenerators(TENGs)have shown superior performance.Multiple reports of electrospinning(ES)-based TENGs have been reported,but there is a lack of deep analysis of the designing method from microstructure,limiting the creative of new ES-based TENGs.Most TENGs use polymer materials to achieve corresponding design,which requires structural design of polymer materials.The existing polymer molding design methods include macroscopic molding methods,such as injection,compression,extrusion,calendering,etc.,combined with liquid-solid changes such as soluting and melting;it also includes micro-nano molding technology,such as melt-blown method,coagulation bath method,ES method,and nanoimprint method.In fact,ES technology has good controllability of thickness dimension and rich means of nanoscale structure regulation.At present,these characteristics have not been reviewed.Therefore,in this paper,we combine recent reports with some microstructure regulation functions of ES to establish a more general TENGs design method.Based on the rich microstructure research results in the field of ES,much more new types of TENGs can be designed in the future.

“项目治国”与“突击花钱”

"项目治国"是指大量财政支出采取项目支出的形式。项目支出易出现实际进度滞后于预算安排,随着项目支出比重增加,财政支出预算执行进度易出现"前低后高"从而产生"突击花钱"现象。基于省级面板数据的计量分析发现:项目支出比重越高,第1季度、上半年预算执行进度越慢,第4季度和12月份支出比重越高,验证了理论预测。人民代表大会开会时间、预算编制质量、转移支付依赖度以及舆论关注所产生的压力,对于"突击花钱"现象也有一定影响。

Inter-group associations in Mongolian gerbils:Quantitative evidence from social network analysis

Animals often interact non-randomly with conspecifics,and association preferences can differ across life-histo­ry stages to maximize individuals’fitness.Mongolian gerbils(Meriones unguiculatus)are a social rodent that live in highly seasonal habitats and display seasonal fluctuations in population density,growth rate and the size of overlapped home ranges.Nevertheless,whether gerbils modify their social relationships at different life-his­tory stages remains unknown.Here,we used social network analysis to examine whether social associations dif­fer between the sexes and between life-history stages in a wild population of Mongolian gerbils.We quantified social attributes at both group level(assortativity)and individual level(social differentiation and degree,close­ness and betweenness centrality);these attributes reflect individuals’social preferences and their potential influ­ence on others in the network.We found that both male and female gerbils established fewer inter-group social connections during the food-hoarding season than during the breeding season,revealing constraints on sociali­ty.Similarly,during the food-hoarding season,degree centrality and social differentiation increased significant­ly whereas closeness and betweenness centrality decreased significantly.Together,these results suggest that ger­bils have relatively more partners and preferred associations and decreased influence over others in the network during the food-hoarding season.In addition,we found no significant difference in any of the social attribute be­tween males and females,but there was a significant interaction effect between sex and season on degree,close­ness and betweenness centrality.Our results demonstrate that Mongolian gerbils adjust their association strat­egies to adapt to the changes of life history.Such adjustments may balance the costs/benefits associated with survival and reproduction.

Effects of short photoperiod on energy intake,thermogenesis,and reproduction in desert hamsters(Phodopus roborovskii)

Desert hamsters(Phodopus roborovskii)are the least known species in the genus Phodopus with respect to ecology and physiology,and deserve scientific attention,particularly because of their small body size.Here,the responses of energy metabolism and reproductive function to short photoperiods in desert hamsters were investigated.Male and female desert hamsters were acclimated to either long day(LD)(L:D 16:8 h)or short day(SD)photoperiods(L:D 8:16 h)for three months,and then the females were transferred back to an LD photoperiod for a further five months,while at the end of the SD acclimation the males were killed and measurements were taken for serum leptin as well as molecular markers for thermogenesis.We found that like the other two species from the genus Phodopus,the desert hamsters under SD decreased body mass,increased adaptive thermogenesis as indicated by elevated mitochondrial protein content and uncoupling protein-1 content in brown adipose tissue,and suppressed reproduction compared to those under LD.However,different from the other two species,desert hamsters did not show any differences in energy intake or serum leptin concentration between LD and SD.These data suggest that different species from the same genus respond in different ways to the environmental signals,and the desert adapted species are not as sensitive to change in photoperiod as the other two species.

Impairment of cellular and humoral immunity in overweight Mongolian gerbils (Meriones unguiculatus)

Animal immunity is usually impaired in obesity.We know little about the effect of being overweight or obese on the immune function of wild rodents.The present study is aimed to test the hypothesis that immunity is suppressed in overweight Mongolian gerbils(Meriones unguiculatus).In the study,16 overweight(body mass:90.8-127.6 g)and 16 lean gerbils(body mass:60.5-77.7 g)were randomly selected from a total of 174 male gerbils(body mass range:55.8-144.7 g).Half of the overweight and lean males were injected with sterile saline;the others were immunochallenged(IC)with phytohaemagglutinin and keyhole limpet hemocyanin to assess cellular and humoral immunity,respectively.Body fat mass,wet and dry spleen mass,leukocyte counts,blood glucose levels and serum leptin levels were significantly higher in the overweight gerbils than in the lean gerbils.However,phytohemagglutinin response indicative of cellular immunity and immunoglobulin G concentrations was significantly lower in the IC overweight gerbils than in the IC lean gerbils.These results indicate that cellular and humoral immunity are impaired in the overweight gerbils.Excessive body fat mass,higher leukocyte counts and serum leptin levels imply that overweight gerbils are in a low grade inflammatory state.

Visual comfort is affected by urban colorscape tones in hazy weather

PeopLe＇s visual perception and recognition of urban coLorscape tones change significantly in hazy weather. A psychoLogicaL experiment is conducted in this study to investigate visual comfort related to commercial and residential buildings. Visual observations are performed on the tones of an urban coLorscape during hazy weather and air poLLution in Harbin, China. Fifty-eight color samples selected through an orthogonaL method are evaluated through a Ukert scale by 30 subjects in a Laboratory setting. Statistical analysis is performed with the maximal information coefficient and R Language. Experimental results show that the changing threshold values of color tones are related to the visual comfort LeveLs of the subjects. The influence of the three factors of color tones on visual comfort Level is reLativeLy independent, and the effects of value and chroma contrast on color comfort Level are greater than that of hue contrast in hazy weather. Furthermore, the comfort recognition threshold values of color tones in hazy weather are determined through data comparisons and analyses.

Role of transient receptor potential vanilloid-1 in behavioral thermoregulation of the Mongolian gerbil Meriones unguiculatus

Ambient temperature considerably affects the physiology and behavior of mammals.Thermosensory and thermoregulatory abilities play an important role in the response to changing ambient temperature in endotherms.However,the molecular mechanisms of behavioral thermoregulation remain poorly understood.Transient receptor potential vanilloid-1(TRPV1)is activated by changes in ambient temperature and is involved in acute thermoregulation.Here,we aimed to determine whether TRPV1 is involved in behavioral thermoregulation in wild rodents by conducting 2 experiments.In the first,42 adult Mongolian gerbils(Meriones unguiculatus;14 per treatment)were randomly assigned to 3 housing temperatures(4,23,and 36℃for 4 weeks.In the second,20 gerbils(10 per treatment)were randomly injected with capsaicin(TRPV1 agonist)or AMG517(TRPV1 antagonist).The results showed a significant decrease in food intake and non-shivering thermogenesis in the gerbils housed at 36℃.Additionally,there was a significant increase in the preference of gerbils housed at 4℃ to low temperatures.The expression of TRPV1 protein in the brown adipose tissue(BAT)and liver was significantly positively correlated with that of protein kinase A(PKA).The expression of TRPV1 and PKA proteins in the BAT was positively correlated with the temperature preference of the gerbils.The gerbils injected with capsaicin preferred significantly lower temperatures than the control group gerbils.These findings suggest that TRPV1 and PKA are involved in behavioral thermoregulation in Mongolian gerbils.

Variation of food availability affects male striped hamsters(Cricetulus barabensis)with different levels of metabolic rate

In the present study,we examined metabolic,morphological and neurochemical changes in male striped hamsters(Cricetulus barabensis)in response to variations in food availability.Males with low and high levels of metabolic rate(MR:L-MR and H-MR,respectively),defined by their activity MR,were compared.In Experiment 1,36-h food deprivation was found to significantly decrease MR levels,body fat content,mass of small and large intestines,and leptin gene expression in the white adipose tissues in male hamsters.Interestingly,L-MR males displayed decreased MR during both the day and night phases of circadian cycles,whereas H-MR males only showed a decrease in MR during the day(resting phase).These data indicate that individual differences in physical activity were associated with animals’different metabolic responses to food deprivation.In Experiment 2,both groups of males went through a 4-week fasting and re-feeding(re)paradigm.H-re males showed a persistent high level of MR,with decreased body fat content and a trending decrease in leptin mRNA expression,compared to L-re males.Together,our data indicate that male striped hamsters with different levels of physical activity display altered,adaptive changes in response to variations in food availability.The neurochemical involvement of such adaptive changes needs to be further studied.

Implication of metabolomic profiles to wide thermoneutral zone in Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils(Meriones unguiculatus)have evolved a wide thermoneutral zone(26.5-38.9°C)and high upper critical temperature,and appear to have a high tolerance for heat exposure.Here,we use a metabolom­ic approach to measure global metabolite profiles for gerbils between lower(27°C)and upper critical tempera­tures(38°C)to investigate the role of metabolomic characterization in maintaining basal metabolic rates within a wide thermoneutral zone.We found that in serum and liver,14 and 19 metabolites were significantly altered,respectively.In the aerobic respiration-related tricarboxylic cycle(TCA),5 intermediates(isocitric acid,cis-ac­onitic acid,α-ketoglutaric acid,fumaric acid and malic acid)were increased in serum in 38°C animals;how­ever,no such increase was found in the liver.A stable level of hepatic TCA cycle intermediates may be relat­ed to the steady state of aerobic respiration at 38°C.Metabolomic results also revealed that acute heat exposure caused increased oxidative stress and low molecular weight antioxidants in Mongolian gerbils.Increased me­thionine and 2-hydroxybutyrate suggest an accelerated synthesis of glutathione.Increased urate and its precur­sors,inosine and hypoxanthine,were detected at 38°C.Glucuronate,threonate and oxalate involved in ascor­bate synthesis and degradation were increased in serum at 38°C.In conclusion,although dramatic metabolomic variation was found,a stable hepatic TCA cycle may contribute to maintaining a constant basal metabolic rate within a wide thermoneutral zone in Mongolian gerbils.

Photoperiodic refractoriness in energy balance： a specific pattern in Mongolian gerbils (Meriones unguiculatus)

Dear Editor,Small mammals inhabiting temperate and arctic zone have evolved seasonal life-history traits, such as seasonal body mass cycle and seasonal reproduction. Photoperiod delivers an unambiguous cue to this seasonal acclimatization in most small mammals. Some species lose body mass, and some others increase body mass in short day (SD) compared to those in long-day (LD) acclimation. The variation in body mass is due to the balance of energy intake and expenditure.

Low temperature fabrication for high-performance semitransparent CsPbI_(2)Br perovskite solar cells

All-inorganic CsPbI_(2)Br perovskite with suitable bandgap and excellent thermal stability has been reported as the most promising candidate for efficient perovskite solar cells (PSCs). However, the high annealing temperature (> 250 ℃) and poor stability of α-CsPbI_(2)Br greatly limit the future application in photovoltaic field. Herein, a facile method is reported to prepare α-CsPbI_(2)Br perovskite film with high stability at low temperature (70 ℃) by incorporating a small amount of γ-aminobutyric acid (GABA) in the precursor solutions. The devices exhibit reproducible photovoltaic performance with a champion efficiency up to 15.16%, along with the excellent stability, maintaining more than 80% of its initial efficiency after stored in ambient condition for 600 h without any encapsulation. Most importantly, the method enables fabrication of semitransparent CsPbI_(2)Br PSCs with a PCE of 6.76%, as well as an average visible transparency (AVT) of 25.38%. To the best of our knowledge, this is the first attempt to apply CsPbI_(2)Br to the semitransparent solar cells.

On the winter enhancement of adaptive humoral immunity: hypothesis testing in desert hamsters (Phodopus roborovskii: Cricetidae, Rodentia) kept under long-day and short-day photoperiod

We tested the winter immunity enhancement hypothesis(WIEH)on male desert hamsters(Phodopus roborovskii)kept under long-day(LD)and short-day(SD)photoperiods.We assumed that under SD in a laboratory,the adaptive humoral immune responsiveness to the antigenic challenge would be enhanced due to the lack of winter physical stressors and food shortages and/or because of the action of an endogenous winter bolstering mechanism,while under LD the immune responsiveness would be suppressed by the activity of the reproductive system.The results support the WIEH in part.We did not find a difference in antibody production in response to sheep erythrocytes between SD and LD hamsters,but SD males had the lower number of granulocytes and the higher number of lymphocytes in white blood cell counts.Reproductive activity was lower in SD males.These males demonstrated an increase in their mass-specific resting metabolic rate,their mass-specific maximal metabolic rate and their level of cortisol.The result of a generalized linear model analysis indicates the negative effect on secondary immunoresponsiveness to sheep erythrocytes of mid-ventral gland size,the organ characterizing individual reproductive quality,and designates a tradeoff between antibody production and reproductive effort.The mass-independent maximal metabolic rate also negatively affected antibody production,indicating a tradeoff between maximal aerobic performance and the adaptive immune function.The higher stress in SD males seems to be the most likely reason for the lack of the effect of daylight duration on antibody production.