Wyniki wyszukiwania - BazTech

1

Experimental study of compressive failure of concrete under static and dynamic loads

Liu L., An H. M.

Archives of Civil Engineering

|

2020

|

Vol. 66, nr 3

427--441

EN

The fracture and fragmentation of concrete under static and dynamic loads are studied. The uniaxial compressive strength test is employed to study the concrete behavior under static loads while the split Hopkinson pressure bar is used to study the dynamic behavior of the concrete under static loads. The theories for acquiring the stress, strain and strain rate of the concrete in the dynamic test by Hopkinson pressure bar has been introduced. The fracture patterns of the concrete in the uniaxial compressive test have been obtained and the static concrete compressive strengths have been calculated. The fracture patterns of the concrete in the uniaxial compressive test have been obtained and the static concrete compressive strengths have been calculated. The fracture and fragmentation of the specimen under dynamic loads have been acquired and the stress-strain curves of concrete under various impact loads are obtained. The stress-strain curve indicates a typical brittle material failure process which includes existing micro-fracture closure stage, linear-elastic stage, nonlinear-elastic stage, and post-failure stages. The influence of the loading rate for the compressive strength of the concrete has compared. Compared with the concrete under static loads, the dynamic loads can produce more fractures and fragments. The concrete strength is influenced by the strain rate and the strength increases almost linearly with the increase of the strain rate.

2

Numerical study of dynamic behaviors of concrete under various strain rates

An H. M., Liu L.

Archives of Civil Engineering

|

2019

|

Vol. 65, nr 4

21--36

EN

As the dynamic behavior of the concrete is different from that under static load, this research focuses on the study of dynamic responses of concrete by simulating the split Hopkinson pressure bar (SHPB) test. Finite element code LS-DYNA is used for modeling the dynamic behaviors of concrete. Three continuous models are reviewed and the Holmquist-Johnson-Cook model (HJC) is introduced in detail. The HJC model which has been implemented in LS-DYNA is used to represent the concrete properties. The SHPB test model is established and a few stress waves are applied to the incident bar to simulate the dynamic concrete behaviors. The stress-strain curves are obtained. The stress distributions are analyzed. The crack initiation and propagation process are described. It is concluded that: the HJC model can modeling the entire process of the fracture initiation and fragmentation; the compressive of the concrete is significantly influenced by the strain rates.

3

Analysis of an N-policy GI/M/1 queue in a multi-phase service environment with disasters

Jiang T., Ammar S. I., Chang B., Liu L.

International Journal of Applied Mathematics and Computer Science

|

2018

|

Vol. 28, no. 2

375--386

EN

This paper investigates an N-policy GI/M/1 queue in a multi-phase service environment with disasters, where the system tends to suffer from disastrous failures while it is in operative service environments, making all present customers leave the system simultaneously and the server stop working completely. As soon as the number of customers in the queue reaches a threshold value, the server resumes its service and moves to the appropriate operative service environment immediately with some probability. We derive the stationary queue length distribution, which is then used for the computation of the Laplace– Stieltjes transform of the sojourn time of an arbitrary customer and the server’s working time in a cycle. In addition, some numerical examples are provided to illustrate the impact of several model parameters on the performance measures.

4

Study on the Rotor Spinning Technology of Cotton Stalk Bark Fibers/Cotton Fibers

Li L., Liu L., Qin C.

Fibres & Textiles in Eastern Europe

|

2018

|

Vol. 26, no. 6 (132)

68--70

EN

The length difference and low flexibility of cotton stalk bark fibers make fiber spinning difficult. In this work, cotton stalk bark fibers that were directly from degummed cotton stalk bark were wetted, carded and softened before sliver-marking, and then they were blended with cotton fibers for carding and spinning in various blending ratios. The results showed that a reasonable open roller speed was 6000 rpm for blending ratio 50/50, 7000 rpm for blending ratio 35/65, and 8000 rpm for blending ratio 20/80. The minimum yarn linear density was 60 tex for blending ratio 50/50, 50 tex for blending ratio 35/65, and 40 tex for blending ratio 20/80.

PL

Różnica długości i niska elastyczność włókien z kory szypułkowej bawełny utrudniają przędzenie włókien. W pracy, włókna z kory szypułkowej bawełny, które były bezpośrednio odśluzowane z bawełnianej szypułki, zwilżono i zmiękczono, a póżniej zmieszano z włóknami bawełnianymi następnie zgrzeblono i przędzono w różnych stosunkach mieszania. Wyniki wykazały, że optymalna prędkość wynosiła 6.000 obrotów/minutę dla stosunku mieszania 50/50, 7.000 obrotów/minutę dla stosunku mieszania 35/65 i 8.000 obrotów na minutę dla stosunku mieszania 20/80. Minimalna gęstość liniowa przędzy wynosił i czystej bawełnya 60 tex dla stosunku mieszania 50/50, 50 tex dla stosunku mieszania 35/65 i 40 tex dla stosunku mieszania 20/80.

5

A novel reliability model for multi-component systems subject to multiple dependent competing risks with degradation rate acceleration

Zhang Y., Ma Y., Liu L., Ouyang L.

Eksploatacja i Niezawodność

|

2018

|

Vol. 20, no. 4

579--589

EN

The purpose of this paper is to establish a new reliability model of the system subject to multiple dependent competing risks. For a system subject to multiple dependent competing risks, the total degradation consists of natural degradation amount and sudden degradation increments (SDIs) caused by random shocks arriving at the system. Most researchers on this topic only focus on the SDIs. However, the impact of random shocks on degradation rate is ignored. In this paper, a novel reliability model considering degradation rate acceleration (DRA) caused by random shocks is proposed, in which the degradation model is based on the degradation path. The dependence relationship between multiple degradation processes is dealt with by copula method, and the arrival time of shocks is assumed to follow a non-homogeneous Poisson process (NHPP). Finally, the effectiveness of the proposed reliability model is demonstrated by an example of a series system. Moreover, the effect of model parameters is evaluated through sensitivity analysis.

PL

Celem niniejszej pracy było stworzenie nowego modelu niezawodności systemu narażonego na liczne zależne ryzyka konkurujące. W przypadku systemu eksponowanego na wiele zależnych ryzyk konkurujących, na wartość całkowitą degradacji składa się wartość degradacji naturalnej oraz wartość nagłych przyrostów degradacji (sudden degradation increments, SDI) powodowanych przez losowe zaburzenia systemu. Większość badaczy tej tematyki koncentruje się wyłącznie na SDI, ignorując tym samym wpływ zaburzeń losowych na tempo degradacji. W niniejszym artykule zaproponowano nowy model niezawodności uwzględniający przyspieszenie tempa degradacji powodowane zaburzeniami losowymi, w którym model degradacji opiera się na krzywej degradacji. Zależność między mnogimi procesami degradacji rozpatrywano za pomocą metody funkcji kopuły przy założeniu, że czas wystąpienia zaburzenia odpowiada niejednorodnemu procesowi Poissona. Skuteczność proponowanego modelu niezawodności zademonstrowano na przykładzie systemu szeregowego. Ponadto, wykorzystano analizę czułości do oceny wpływu parametrów modelu na niezawodność systemu.

6

Numerical Simulations of the Effects of Droplet Size and Concentration on Vapour-Droplet JP-10/Air Detonations

Liu L., Zhang Q.

Central European Journal of Energetic Materials

|

2018

|

Vol. 15, no. 1

175--190

EN

Two-dimensional simulations were conducted for JP-10 mono-dispersed vapour-droplet detonation in air, based on the detonation mechanism for clouds and validation of the extending critical droplet size limits in previous tests. In the simulations, the discrete phase model combined with the droplet evaporation and droplet breakup models was used. Utilizing a wide range of mono-dispersed droplet sizes and initial droplet concentrations, all cases of JP-10 droplets with a certain amount of pre-vaporized fuel can successfully achieve the deflagration to detonation transition. Detonation velocities at the equivalent concentration with droplet diameters no larger than 50 μm are in good agreement with the theoretical detonation velocities. The effects of droplet size and initial droplet concentration on the detonation behaviour were also investigated. Detonation velocities attained with droplet diameters below 50 μm appear to decrease very slightly with droplet size, but are almost equal to the velocity in gases. When the droplet diameter is above 50 μm, there is a decrease in simulated detonation velocity compared with fine droplets, and no secondary pressure peak was observed. For fuel-rich combustion, detonation velocities decrease rapidly with an increase in initial droplet concentration, and post-wave pressure fluctuation was obviously irregular, caused by the secondary local explosion of the droplets.

7

Effects of Polymeric Binders on the RDX-based Explosive Response Character under Slow Cook-off Conditions

Yan X., Li X. D., Zhang Y. R., Liu L., Zhang X. M., Tan Y. X., Wang H., Wang X. Q.

Central European Journal of Energetic Materials

|

2018

|

Vol. 15, no. 2

339--350

EN

Due to safety requirements, insensitive behaviour under slow thermal heating (cook-off) conditions is a desirable behaviour for today’s munitions. In this paper a cook-off device is designed to test two groups of RDX-based PBX explosives. In the first group the binder type was varied and in the second group the binder content of the RDX-based explosive was changed. Eleven samples were examined in order to evaluate the influence of four different binders and seven different binder contents on the shell deformation and the degree of the involved reaction. The test results showed that the degree of the reaction can be improved by changing the binder content, but not by the binder type. This phenomenon was explained by the thermal-conduction theory.

8

Comparison of grinding characteristics in high-pressure grinding roller (HPGR) and cone crusher (CC)

Liu L., Tan Q., Liu L., Li W., Lv L.

Physicochemical Problems of Mineral Processing

|

2017

|

Vol. 53, iss. 2

1009--1022

EN

We comparatively studied the ball mill grinding characteristics of comminuted hematite products using a high-pressure grinding roll (HPGR) and a conventional cone crusher (CC). The major properties, including grinding kinetics and technical efficiency (Et), were investigated. The parameters in m-th order grinding kinetics were analyzed, and grinding specific rates were visualized. Ore particles experienced three inherent stages in ball grinding mills, that is i) rapid grinding of coarse fraction, ii) dynamic grinding of medium size fraction, and iii) single grinding of medium size fraction. Particles with size -0.043+0.031 mm were used into dynamic grinding stage earlier than particles -0.105+0.043 mm, and then over-grinding of fines occurred easily. Compared with CC products, HPGR products had significantly shorter turning time points in three breakage stages, implying that HPGR products were ground faster with earlier occurrence of fines over-grinding. HPGR products gave lower Et at a decreasing rate than the CC products for -2.0 mm and -0.5 mm feeds. Then, it showed a slightly higher value of Et for -2.0+0.5 mm feed. This indicated that fines over-grinding in HPGR full-size products were more serious under the condition of coarse grinding, whereas the efficiency was higher, and over-grinding weakened significantly in HPGR coarse products because of screening-out fines.

9

Characterization of Dinophysis acuminata from the Yellow Sea, China, and its response to different temperatures and Mesodinium prey

Gao H., An X., Liu L., Zhang K., Zheng D., Tong M.

Oceanological and Hydrobiological Studies

|

2017

|

Vol. 46, No. 4

439--450

EN

Dinophysis species are distributed worldwide and cause diarrheic shellfish poisoning (DSP). This paper documents the first successful culture of a Dinophysis (DAYS01) strain taken off Xiaoping Island, the Yellow Sea, China. The strain was identified as Dinophysis acuminata Claparède & Lachmann by morphological and phylogenetic analysis. The effects of temperature and different Mesodinium prey on the physiological and toxigenic characteristics of D. acuminata DAYS01 were also investigated. The results showed that the toxin concentration (toxin amount per ml of culture) increased with an increase in cell densities. Okadaic acid (OA), dinophysistoxin 1 (DTX1) and pectenotoxin 2 (PTX2) were the major toxin components of DAYS01, with the highest recorded toxin content of 5.66, 0.56 and 192.87 ng ml-1 culture medium, respectively. The prey type significantly influenced the growth yield in Dinophysis cultures. There was an effect of prey on the total toxin content, suggesting that the origin or strain of ciliate directly impacted the D. acuminata blooms and the overall toxin concentration in the system.

10

Exact solution to the structural instability of a parallel array of mutually attracting identical simply-supported plates

Wang X., Liu L.

Archives of Mechanics

|

2017

|

Vol. 69, nr 3

243--256

EN

By means of the theory of elasticity, we investigate the structural instability of a parallel array of identical simply-supported plates. One plate interacts with the neighboring plates through surface attractive forces. The proposed method is based on the 2 × 2 transfer matrix for a plate and on the solution of the generalized eigenvalue problem for the plate array. Analytical expressions of the critical interaction coefficients for two, three and four interacting plates are obtained when the end-effect of the plates at the ends of the parallel array and the surface energy of the plates are ignored. The influence of the end-effect and surface energy on the critical interaction coefficient is also numerically studied. Our solution is valid whether the plates are thin or extremely thick.

11

Volcanic ash cloud detection from MODIS image based on CPIWS method

Liu L., Li Ch., Lei Y., Yin J., Zhao J.

Acta Geophysica

|

2017

|

Vol. 65, no. 1

151--163

EN

Volcanic ash cloud detection has been a difficult problem in moderate-resolution imaging spectroradiometer (MODIS) multispectral remote sensing application. Principal component analysis (PCA) and independent component analysis (ICA) are effective feature extraction methods based on second-order and higher order statistical analysis, and the support vector machine (SVM) can realize the nonlinear classification in low-dimensional space. Based on the characteristics of MODIS multispectral remote sensing image, via presenting a new volcanic ash cloud detection method, named combined PCA-ICA-weighted and SVM (CPIWS), the current study tested the real volcanic ash cloud detection cases, i.e., Sangeang Api volcanic ash cloud of 30 May 2014. Our experiments suggest that the overall accuracy and Kappa coefficient of the proposed CPIWS method reach 87.20 and 0.7958%, respectively, under certain conditions with the suitable weighted values; this has certain feasibility and practical significance.

12

Dark and singular optical solitons with competing nonlocal nonlinearities

Zhou Q., Liu L., Zhang H., Mirzazadeh M., Bhrawy A. H., Zerrad E., Moshokoa S., Biswas A.

Optica Applicata

|

2016

|

Vol. 46, nr 1

79--86

EN

In this work, we study the dynamics of optical solitons in a synthetic nonlocal nonlinear media. The nonlinear dynamical model which describes the propagation of optical solitons in the weakly nonlocal nonlinear media with parabolic law nonlinearity is investigated analytically. The tool of integration that is the Riccati equation mapping approach is introduced to extract exact traveling wave solutions. As a result, an explicit dark soliton, singular soliton and periodic solutions are derived.

13

Image fusion for travel time tomography inversion

Yin X., Liu L., Zhao X., Ashraf M. A.

Polish Maritime Research

|

2015

|

S 1

149--156

EN

The travel time tomography technology had achieved wide application, the hinge of tomography was inversion algorithm, the ray path tracing technology had a great impact on the inversion results. In order to improve the SNR of inversion image, comprehensive utilization of inversion results with different ray tracing can be used. We presented an imaging fusion method based on improved Wilkinson iteration method. Firstly, the shortest path method and the linear travel time interpolation were used for forward calculation; then combined the improved Wilkinson iteration method with super relaxation precondition method to reduce the condition number of matrix and accelerate iterative speed, the precise integration method was used to solve the inverse matrix more precisely in tomography inversion process; finally, use wavelet transform for image fusion, obtain the final image. Therefore, the ill- conditioned linear equations were changed into iterative normal system through two times of treatment and using images with different forward algorithms for image fusion, it reduced the influence effect of measurement error on imaging. Simulation results showed that, this method can eliminate the artifacts in images effectively, it had extensive practical significance.

14

Direct synthesis of dimethyl carbonate and propylene glycol using potassium bicarbonate as catalyst in supercritical CO2

Wen Y., Zhang R., Cang Y., Zhang J., Liu L., Guo X., Fan B.

Polish Journal of Chemical Technology

|

2015

|

Vol. 17, nr 1

62--65

EN

The improved one-pot synthesis of dimethyl carbonate and propylene glycol from propylene oxide, supercritical carbon dioxide, and methanol with potassium bicarbonate as the catalyst has been reported in this paper. As far as we know, it is the first time to use potassium bicarbonate only as the catalyst in the production process which is simple and cheap. Satisfactory conversion rate of propylene oxide and yield of the products could be achieved at the optimized conditions with quite a small amount of by-products. Our new method offers an attractive choice for the production of dimethyl carbonate in large-scale industry efficiently and environmental friendly.

15

A novel logic-based approach for failure modes mitigation control and quantitative system reliability analyses

Yang D., Ren Y., Wang Z., Liu L., Sun B.

Eksploatacja i Niezawodność

|

2015

|

Vol. 17, no. 1

100--106

EN

The core idea of reliability design is to mitigate the product’s failure modes. However, for the cross-links among potential failure modes of a complex product, it is very difficult to establish the mapping relationship between failure modes mitigation and quantitative values of reliability, and the decision of failure modes mitigation have to be performed by virtue of experience, which always increase design period. In order to solve these problems, a novel logic-based approach for failure modes mitigation control and quantitative system reliability analyses is provided. Firstly, a hybrid of active and passive control process of reliability design is proposed. Secondly, a novel concept of failure modes correlation set (FMCS) and a determination approach based on deductive theory are presented. According to the changes in failure modes probabilities of occurrence, the reliability formulas of the components and assemblies are provided to depict the effects of failure mode mitigation on reliability of components and assemblies. And then the FMCS mitigation sequence is decided to determine reliability design activities. Thirdly, a closed control process of FMCS mitigation is provided integrated with logic decision method. By exposing the design of a helicopter fuel system, the present study demonstrates that all approaches are feasible, and the relationship between reliability parameters and qualitative design exists. Hence the failure modes mitigation could be controlled for the achievement of quantitative reliability requirements.

PL

Podstawowym problemem w procesie projektowania niezawodności jest ograniczenie przyczyn uszkodzeń produktu. Jednakże, w przypadku sieci połączeń pomiędzy możliwymi przyczynami uszkodzeń złożonego produktu, trudno jest ustalić mapę zależności pomiędzy ograniczaniem przyczyn uszkodzeń i ilościowymi wartościami niezawodności, a decyzje względem ograniczania przyczyn uszkodzeń muszą bazować na własnym doświadczeniu, co znacznie wydłuża okres projektowania. W celu rozwiązania powyższych problemów, zaproponowano oryginalną, opartą na logice, metodę kontroli ograniczania przyczyn uszkodzeń i ilościowej analizy niezawodności systemu. Na wstępie, zaproponowano mieszany proces aktywnej i pasywnej kontroli niezawodności projektu. Następnie, zaprezentowano oryginalną koncepcję zbioru korelacji przyczyn uszkodzeń (FMCS) i metodę oznaczania opartą o teorię dedukcji. Na podstawie zmian dotyczących prawdopodobieństwa występowania przyczyn uszkodzeń, określono wzory niezawodności części i układów w celu pokazania wpływu ograniczania przyczyn uszkodzeń na niezawodność części i układów. Określono następnie ograniczającą sekwencję FMCS, ażeby ustalić założenia dla projektowania niezawodności. Na koniec zaprezentowano zamknięty proces kontroli ograniczania FMCS w powiązaniu z logiczną metodą podejmowania decyzji. Analizując pod tym kątem projekt systemu paliwowego helikoptera, wykazano w niniejszej pracy przydatność wszystkich powyższych metod, jak również związek pomiędzy parametrami niezawodności a projektowaniem jakościowym. Dlatego też ograniczanie przyczyn uszkodzeń powinno być kontrolowane w celu osiągnięcia wymaganej niezawodności ilościowej.

16

Deliberations about three-phase PLL technologies applied to a grid control of the renewable power system

Liu L., Liu C.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2015

|

Vol. 63, nr 1

261--267

EN

An efficient phase locked loop (PLL) method is very important to improve the grid-connected efficiency and the locked speed of frequency, phase, and voltage. However, most of literatures only introduce one PLL or one modified PLL method. There are many grid faults due to the grid connection to the renewable power generating system. A comparison and analysis is very important to select the most effective PLL technology for the grid-connected control of the renewable power system. Three PLL technologies are compared at different grid faults, such as single phase voltage drop, two phase voltage drop, frequency deviation, and voltage distortion. Simulation results indicated that different PLL methods have different locked performances at different grid faults.

17

Electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations

Zheng S K, Wu G., Zhang S., Su J., Liu L.

Materials Science Poland

|

2014

|

Vol. 32, No. 1

93--97

EN

The electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations were calculated using the first-principles based on the density functional theory. The calculated results show that the forbidden band widths of Hgdoped anatase TiO2 widened along with the increase of O vacancy concentration, which is responsible for the blue shift in the absorption edges. It can be deduced from the present study that the Hg-doped TiO2 samples prepared in the experimental research contain a certain quantity of O vacancies.

18

Preparation of molecularly imprinted polymer for chiral recognition of racemic 1,1′-binaphthalene-2,2′-diamine by HPLC

Dong H., Wang Y., Ou Y., She J., Shen X., Li J., Zhang Ch., Liu L.

Acta Chromatographica

|

2014

|

Vol. 26, no. 4

683--693

EN

Molecularly imprinted polymers (MIPs) were synthesized by imprinting a new template—S(-)-1,1′-binaphthalene-2,2′-diamine (S-DABN) and applied as chiral stationary phases for chiral separation of DABN racemates by high-performance liquid chromatography (HPLC). The influence of some key factors on the chiral recognition ability of MIPs, such as the type of functional monomers and porogen and the molar ratio of template to monomer, was systematically investigated. The chromatographic conditions, such as mobile phase composition, sample loading, and flow rate, were also measured. The chiral separation for DABN racemates under the optimum chromatographic conditions by using MIP chiral stationary phase (CSP) of P3, prepared with the S-DABN/MAA ratio = 1/4 and used acetonitrile (2 mL) and chloroform (4 mL) as porogen, showed the highest separation factor (2.14). Frontal analysis was used to evaluate affinity to the target molecule of MIPs. The binding sites (Bt) of MIPs and dissociation constant (Kd) were estimated as 4.56 μmol g−1 and 1.40 mmol L−1, respectively. In comparison with the previous studies, this approach had the advantages, such as the higher separation factor, easy preparation, and cost-effectiveness, it not only has the value for research but also has a potential in industrial application.

19

Frequency Estimation Algorithms by Fusion Spectra of Multi-section Sinusoids

Xiao W., Tu Y., Liu L., Shen Y., Zhang L.

Przegląd Elektrotechniczny

|

2013

|

R. 89, nr 3b

246--253

EN

For achieving a more precise frequency estimation of a short sinusoid at low SNR, a algorithm based on fusion spectra of Multi-section Sinusoids(M-sinusoids) was proposed. In order to solve the discontinuous phases problem of M-sinusoids, the Optimization Weighted-Accumulation (OW-A) spectrum was gained through weighted-accumulation spectra of M-sinusoids by the designed weighted factor. The correlation spectrum, which could inherit the narrow and high main-lobe of the OW-A spectrum, and the good noise immunity of the accumulation spectrum of M-sinusoids, was constructed by correlation OW-A spectrum and the accumulation spectrum. Therefore, higher precision frequency estimation could be obtained through spectral peak searching of the correlation spectrum. Moreover, in order to meet the high real-time demand in some fields, a fast algorithm of the proposed algorithm was put forward. This fast algorithm could reduce most computational cost of the proposed algorithm by the following techniques: design a fast DTFT algorithm, reduction dimensions of the weighted fusion spectrum matrix, 1/3 main-lodes correlation of the OW-A spectrum and the accumulation spectrum. Simulations demonstrate the superior performance of the proposed algorithms; the fast algorithm could reduce most calculation of the proposed algorithm with lowering a little frequency estimation precision, and it works better in very low SNR (SNR≤-13dB).

PL

W artykule zaproponowano algorytm estymacji częstotliwości krótkich fal sinusoidalnych o niskim zaszumieniu (SNR). Rozwiązanie bazuje na widmie fuzji M-częstotliowości sinusoid (M-sinusoids). W celu rozwiązania problemu nieciągłości faz M-sinusoid zastosowano współczynniki wagowe zawartości częstotliwości, co pozwoliło na ich optymalizację (ang. Optimization Weighted-Accumulation). Zastosowanie algorytmu pozwala na zwiększenie precyzji estymacji przy jednoczesnym zwiększeniu szybkości wykonania. Wyniki badań symulacyjnych potwierdzają skuteczność działania.

20

Effects of snowpack and litter decomposition on nitrogen dynamics in soil of the alpine zone of the Eastern Tibetan Plateau

Hu X., Wu Y., Wang Q., Liu L., Zuo W.-Q., Shi F.-S., Wu N.

Polish Journal of Ecology

|

2013

|

Vol. 61, nr 2

297--304

EN

Microbes remain active and play an important role in soil nitrogen (N) cycle during the winter in soil of the alpine zone. A shift from microbial N immobilization process dominant during summer to prevailing microbial mineralization process during the winter is observed. Warmer soil under deep snow cover may increase the microbial activity and rate of organic matter decomposition over the winter. Furthermore, severe shortages of dissolved carbon (C) in the winter may cause microbial mortality and lyses. Thus, C limitation on microbial growth and activity may have an important effect on winter N mineralization and even on soil N pools. However, the combined effects of additional organic C (litter inputs) and snow cover on soil N biogeochemical processes in the Tibetan Plateau remain unclear. In the current study, the in situ effects of snowpack and litter decomposition on N dynamics in the alpine zone of the Eastern Tibetan Plateau were investigated. Intact soil core incubations in three different snow regimes (0, 30 and 100 cm depth snow) in the winter were used to solve the problem by measure concentrations of mineral form of soil N. In addition, the litter bag method was used to analyze the litter decomposition over the winter. Our results indicate that the snow cover reduced the ammonium (NH4+-N) content, accelerate N mineralization in soil, and did not significantly change the dissolvable organic nitrogen (DON) and microbial biomass nitrogen (MBN). Meanwhile, snowpack increased the litter N content and accelerated litter decomposition in late winter. Litter addition reduced the MBN and NH4+-N contents in soil, but increased the nitrate (NO3--N) content and net N mineralization, suggesting that N availability to plants during the spring thaw period may be enhanced.