Study of the radial growth response to climate factors at different tree ages is essential for predicting forest dynamics and formulating correct management policies. In this study, we analysed the growth responsiveness of Picea crassifolia to climate conditions, and evaluated its relationship to tree age at the individual tree scale, in the transitional zone between regions affected by the East Asian monsoon and winds blowing from the west (westerlies) in the Qilian Mountains. On three study sites, 150 cores were taken from 75 trees. Pearson correlation coefficients were calculated between the standardized tree-ring series of each core (and chronology) and climatic factors which were utilized to research the climate-growth relationships. Quadratic polynomial fitting was used to test the relationships between tree age, chronological parameters, and the radial growth response to climate. Radial growth was positively influenced by total precipitation for the previous July-September and the current May-July. Additionally, radial growth was negatively correlated with the total monthly precipitation for the current September, and the mean monthly temperature for the previous July. Trees younger than 80 years old showed a stronger response to accumulative precipitation in the previous July-September, those older than 160 years old showed a stronger response to precipitation at the end of current growing season, while those of 140-160 years old showed a weaker response to precipitation in the current May-July.
Ni-Nb-Zr/CaF2 amorphous coating was prepared on the surface of SA283GRA steel by adopting a high-power laser cladding system. The results show that the Ni-Nb-Zr/CaF2 coating obtained by laser cladding has a good metallurgical bonding with the matrix of SA283GRA and the amorphous phase was obtained. The different amorphous content was obtained with varied laser power. With the increase of laser power, the dilution rate of the coating gradually increases, the amorphous phase content in the cladding coating decreased gradually, and crystallization near the substrate is significant in the laser coating. As the cladding coating is far from the substrate, the content of amorphous phase increases gradually, and the cladding coating has high thermal stability. The hardness of the Ni-Nb-Zr/CaF2 amorphous coating prepared by a laser power of 4 kW is up to the highest value of 890 HV, which is about 4.7 times that of the base material. The electrochemical corrosion results show that the corrosion resistance of the amorphous layer is better than that of the substrate in NaCl solution with 3.5% corrosive medium. The Ni-Nb-Zr/CaF2 laser coating has a relatively strong amorphous forming ability.
PL
Amorficzną powłokę Ni-Nb-Zr/CaF2 otrzymano na powierzchni stali SA283GrA metodą natryskiwania laserowego, z wykorzystaniem laserów dużej mocy. Uzyskane wyniki badań wykazały, że powłoka Ni-Nb-Zr/CaF2 charakteryzuje się dobrą przyczepnością do podłoża stalowego SA283GrA, a faza amorficzna jest otrzymywana w strefie przypowierzchniowej. Wykazano, że moc wyładowania laserowego istotnie wpływa na zawartość fazy amorficznej. Wraz ze wzrostem mocy lasera zawartość fazy amorficznej w strefie przypowierzchniowej zmniejsza się stopniowo, a stopień krystalizacji powłoki w pobliżu podłoża wzrasta. Zawartość fazy amorficznej zwiększa się gradientowo w funkcji odległości od podłoża. Największą twardość powłoki amorficznej Ni-Nb-Zr/CaF2 890 HV uzyskano z wykorzystaniem lasera o mocy 4kW, tj. ≈4,7 razy większą w stosunku do materiału podłoża. Wyniki badań odporności korozyjnej metodą elektrochemiczną wykazały, że w roztworze NaCl z 3,5% odporność na korozję strefy przypowierzchniowej zawierającej fazę amorficzną jest większa niż odporność korozyjna podłoża. Wykazano również, że faza amorficzna Ni-Nb-Zr/CaF2 ma stosunkowo dużą zdolność do formowania się w strefie przypowierzchniowej i charakteryzuje się dużą stabilnością temperaturową.
For most precious metal mines, cemented tailings backfill slurry (CTBS) with different cement-sand ratio and solid concentration are transported into the gobs to keep the stability of the stope and mitigate environmental pollution by mine tailing. However, transporting several kinds of CTBS through the same pipeline will increase the risk of pipe plugging. Therefore, the joint impacts of cement-sand ratio and solid concentration on the rheological characteristics of CTBS need a more in-depth study. Based on the experiments of physical and mechanical parameters of fresh slurry, the loss of pumping pressure while transporting CTBS with different cement-sand ratio, flux and solid mass concentration were measured using pumping looping pipe experiments to investigate the joint impacts of cement-sand ratio and solid concentration on the rheological characteristics of CTBS. Meanwhile, the effect of different stopped pumping time on blockage accident was revealed and discussed by the restarting pumping experiments. Furthermore, Fluent software was applied to calculate the pressure loss and velocity distribution in the pipeline to further analysis experimental results. The overall trends of the simulation results were good agreement with the experiment results. Then, the numerical model of the pipeline in the Sanshandao gold mine was conducted to simulate the characteristics of CTBS pipeline transportation. The results show that the pumping pressure of the delivery pump can meet the transportation requirements when there is no blockage accident. This can provide a theoretical method for the parameters optimizing in the pipeline transportation system.
PL
W większości kopalń metali szlachetnych zawiesina zawierająca odpady poflotacyjne wraz z cementem w różnych proporcjach cementu i piasku oraz o różnym stężeniu części stałych transportowana jest do wyrobisk i zrobów, gdzie wykorzystywana jest następnie do stabilizacji w rejonie przodka, ponadto w ten sposób ogranicza się zanieczyszczenie środowiska odpadami poflotacyjnymi. Jednakże przetłaczanie różnych rodzajów zawiesin w tym samym układzie rurociągu zwiększa ryzyko zaczopowania rur. Zbadanie wpływu proporcji cementu do piasku w zawiesinie oraz stężenia części stałych na charakterystykę reologiczną zawiesiny wydaje się kwestią kluczową. W oparciu o badania eksperymentalne fizycznych i mechanicznych parametrów świeżej zawiesiny, dokonano pomiarów spadku ciśnienia pompowania w trakcie przetłaczania zawiesin o zawartości cementu i pisaku w różnych proporcjach, dla różnych natężeń przepływu i stężeń części stałych w eksperymentach z wykorzystaniem linii obiegowej rurociągu. Celem eksperymentu było określenie łącznego wpływu proporcji cementu do piasku oraz stężenia części stałych na właściwości reologiczne zawiesiny. Ponadto, przeanalizowano w jaki sposób długość przerw w procesie przetłaczania wpływa na zwiększenie ryzyka zatkania rur i przeprowadzono eksperymenty polegające na wznowieniu pracy pomp. Analizę wyników eksperymentów uzupełniono poprzez zastosowanie oprogramowania Fluent do obliczenia spadku ciśnienia w rurociągu oraz rozkładu prędkości. Wykazano, że wyniki symulacji pozostawały w dużej zgodności z wynikami eksperymentów. W kolejnym kroku opracowano model numeryczny rurociągu eksploatowanego w kopalni złota Sanshandao dla potrzeb symulacji procesu przetłaczania zawiesiny. Uzyskane wyniki wskazują, że ciśnienie tłoczenia w pompie jest na wymaganym poziomie gdy nie występuje zablokowanie przepływu w rurze, i wykorzystane być mogą jako uzupełnienie teoretycznych metod optymalizacji parametrów układu transportowania i przetłaczania zawiesiny.
Considering the environmental pollution caused by waste rubber, some measures should be taken to improve the utilization rate of waste rubber. In this study, the effect of Ethylene Propylene Diene Monomer (EPDM) particles in the polyurethane (PU) foams on sound absorption behavior is investigated for improving sound environment within vehicles and reducing the environment pollution. EPDM particles of different contents and hardness are used as fillers for producing foams with different pore morphologies and sound absorption properties. The results show that adding EPDM to foam would produce smaller pores, higher density and bigger air-flow resistivity. Simultaneously, there are better sound absorption properties of the PU foam composites in the medium frequency region, and the better value can be obtained at the lower frequency with the content of EPDM increasing. The hardness of EPDM also shows better influence on sound absorption properties, especially in the medium frequency region. It means the foam pore morphologies have influence on sound absorption properties.
5
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Changing localized environmental conditions along altitude gradients could modify the responses of tree xylem structures to climate variations. To explore how trees adapt to local environment and respond to climate variants, we analysed the variation of Picea meyeri xylem tracheid features and the relationships with climate variables along an altitude gradient (1970, 2240, 2490 and 2650 m above sea level) of the Luyashan Mountains in the North China. The results mainly indicated the following: (1) tracheid number and diameter of P. meyeri showed significant differences among the four sites along the altitude gradient; (2) trees at site 2 (2240 m) and site 3 (2490 m) are similar in age, but the xylem tracheid number and diameter of these trees were significantly different, which may indicate different functional adaptation; (3) the relationships between xylem features' residual chronologies and the monthly climate data were inconsistent along altitude gradients, which indicated that the limiting factor of P. meyeri growth along the altitude gradients, shifted from drought stress at lower altitudes to low-temperature stress at higher altitudes.
Width design of the urban rail transit stations circulation facilities is a vital issue. The existing width design approach failed in fully considering the essential factors such as fluctuation in passengers’ arrival process, fluctuation and state-dependence in passengers walking speed and the blocking when passengers’ demand exceeds the capacity of facilities. For this purpose, a PH-based simulation-optimization approach is proposed that fully considers the fluctuation, the state-dependence, Level of Service (LOS) and blocking effect. This novel approach provides automatic reconfiguration of the widths of circulation facilities by a concurrent implementation of a PH-based Discrete-Event Simulation (DES) model and the Genetic Algorithm (GA). The proposed PH-based simulation-optimization approach and the existing design approaches based on the exponential and deterministic models are applied to design the widths of circulation facilities. The results reveal that the circulation facilities designed by the proposed approach have larger widths. Similarly, increase in the SCV of arrival interval results in increasing the widths designed by the proposed approach increase while the widths of the other two approaches stay the same. The width designed of the proposed approach increase at faster rate than that of the other two approach when the passengers’ arrival rate increases.
7
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Grain size dependence of microhardness has been addressed in the bainitic reheated weld metals by in situ observation of morphological evolution and characterization of microstructural development. A higher cooling rate promotes the boundary of smaller prior austenite grains to provide more effective sites for primary bainitic ferrite nucleation, yet a lower cooling rate is increasingly beneficial to sympathetic nucleation as well as impingement of secondary bainitic ferrite. The microstructures, obtained by cooling at a higher rate and composed of abundant lath bainite, are closer to the microstructures in the raw weld metal than those cooled at a lower rate, including lath bainite, acicular ferrite and intercritical ferrite. Microhardness is decisive by prior austenite grain size mainly, as well as microstructures. Smaller grains contribute notably to microhardness, and it is worth stressing that the sizes of smaller grains lie on prior austenite grain boundaries rather than the subboundaries generated by intragranular acicular ferrite and intercritical ferrite.
In this study, an effective optimization approach was proposed to improve acoustical behaviors of PU foams. The important parameters of PU foams: content of water, silicone oil and catalyst A1 were chosen and their effects on sound absorption coefficient and transmission loss of PU foams were studied by using Taguchi methods. In addition, bamboo chips were incorporated into PU foams as fillers to improve the acoustical properties of PU foams. Four controlled factors: the content of water, silicone oil, catalyst A1 and bamboo chips with three levels for each factor were chosen and Taguchi method based on orthogonal array L9 (34) was employed to conduct the experiments. Based on the results of Taguchi’s orthogonal array L9 (34), signal-to noise (S/N) analysis was used and developed to determine an optimal formulation of PU-bamboo-chips foam composites.
Compared with standard vessels, a slender catamaran with a semi-submerged bow (SSB) demonstrates superior seakeeping performance. To predict the motion of an SSB catamaran, computational fluid dynamics methods are adopted in this study and results are validated through small-scale model tests. The pitch, heave, and vertical acceleration are calculated at various wavelengths and speeds. Based on the overset grid and motion region methods, this study obtains the motion responses of an SSB catamaran in regular head waves. The results of the numerical studies are validated with the experimental data and show that the overset grid method is more accurate in predicting the motion of an SSB catamaran; the errors can be controlled within 20%. The movement data in regular waves shows that at a constant speed, the motion response initially increases and then decreases with increasing wavelength. This motion response peak is due to the encountering frequency being close to the natural frequency. Under identical sea conditions, the motion response increases with the increasing Froude number. The motion prediction results, that derive from a shortterm irregular sea state, show that there is an optimal speed range that can effectively reduce the amplitude of motion.
10
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Linking the response of tree growth to global warming is a key to fully appreciating the impact of climate change on forests. To examine the impacts of temperature and precipitation on tree growth, we studied the radial growth of Pinus tabulaeformis along an altitude gradient from 2032 m a.s.l. to 2361 m a.s.l. on the Helan Mountains, which is almost the northwestern limit of P. tabulaeformis distribution in China. The results showed that, radial growth of P. tabulaeformis decreased significantly (P <0.05) at the low altitude (2032 m a.s.l.) and remained almost steady at the middle and high altitude (2200 m a.s.l. and 2361 m a.s.l.) during the past decades, which was attributed to different climate-radial growth relationships at different altitudes. Total precipitation from the previous July to the current June was an important and effective climatic factor for radial growth at all altitudes. Radial growth was negatively correlated with the mean temperature of the current March at the low altitude and was positively and negatively correlated with the mean temperature of the previous October and the current July at the high altitude, respectively. Increasing temperature of the March under the context of global warming was the main reason for growth reduction at the low altitude. Radial growth at the middle and high altitudes didn't suffer from global warming. It was inferred that conifers at low altitudes of the species' dry distribution limit were more vulnerable to global warming. To cope with possible intensified drought in the growing season and growth reduction in the future, thinning and afforestation should be carried out in the forests, especially at low altitudes.
The scratch on a fused silica surface was treated as a chain of connected damage sites and mitigated one after another using CO2 laser irradiation. The optical microscopy image shows that a scratch with the width of about 30 μm and length of several millimeters can be completely mitigated without the formation of debris and bubbles. The mitigated scratch can survive under raster scan laser irradiation with the fluency increased up to 11.0J/cm2 at 3ns and 351nm. On the contrary, the substrate without CO2 laser mitigation is seriously damaged under this irradiation. The light modulation induced by mitigation is much smaller when the scratch is mitigated before being damaged. The light modulation is about 2 when the distance to the mitigated sample is larger than 20cm. The birefringence induced by residual stress in the mitigated scratch is measured. The retardance of the mitigated scratch before being damaged is not visible. Therefore, residual stress in this mitigated scratch before being damaged should be not a critical potential risk in laser damage.
12
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
Describing the dispersion decreasing fiber, a variable-coefficient nonlinear Schrödinger equation is hereby under investigation. Three transformations have been obtained from such a equation to the known standard and cylindrical nonlinear Schrödinger equations with the relevant constraints on the variable coefficients presented, which turn out to be more general than those previously published in the literature. Meanwhile, several families of exact dark-soliton-like and bright-soliton-like solutions are constructed. Also, we obtain some similarity solutions, which can be illustrated in terms of the elliptic and the second Painlevé transcendent equations.
13
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
A good assignment of code reviewers can effectively utilize the intellectual resources, assure code quality and improve programmers’ skills in software development. However, little research on reviewer assignment of code review has been found. In this study, a code reviewer assignment model is created based on participants’ preference to reviewing assignment. With a constraint of the smallest size of a review group, the model is optimized to maximize review outcomes and avoid the negative impact of “mutual admiration society”. This study shows that the reviewer assignment strategies incorporating either the reviewers’ preferences or the authors’ preferences get much improvement than a random assignment. The strategy incorporating authors’ preference makes higher improvement than that incorporating reviewers’ preference. However, when the reviewers’ and authors’ preference matrixes are merged, the improvement becomes moderate. The study indicates that the majority of the participants have a strong wish to work with reviewers and authors having highest competence. If we want to satisfy the preference of both reviewers and authors at the same time, the overall improvement of learning outcomes may be not the best.
The greater the mine, the harder stability control will be. And the conventional rock bolts do not adapt well to the severe rock stress conditions. An ideal bolt having a high resistance and large deformation should be developed. Based on the test results and theoretical study, this paper proposes an energy-absorbing expandable rock bolt, which consists of the bar, sleeve, bolt plate, nut, and bolt end. The anchoring mechanism and its efficiency were systematically analysed in the laboratory and in practice: the anchoring mechanism and supporting density, especially the quantitative relationship, were deduced under the Energy Balance Theory, that is, EB = 1 2 · n · F0 (u0 + 2∆u). As Compared with the conventional bolt and large deformation bolts, the new type of bolt could provide a larger constant resistance, even in the soft rock roadway with large squeezing deformation, the pulling force can be achieved by F = A · σ · f2, it mainly being generated by a normal stress acting on the pore surface. These characteristics are helpful in making the supported roadway safe. The amount of released energy during the large deforming process of the surrounding rock is expressed through conservation of energy, which can provide reference to the quantitative calculation of the bolt supporting system.
The normal modes cannot be extracted even in the Pekeris waveguide when the source-receiver distance is very close. This paper introduces a normal mode extraction method based on a dedispersion transform (DDT) to solve this problem. The method presented here takes advantage of DDT, which is based on the waveguide invariant such that the dispersion associated with all of the normal modes is removed at the same time. After performing DDT on a signal received in the Pekeris waveguide, the waveform of resulting normal modes is very close to the source signal, each with different position and amplitude. Each normal mode can be extracted by determining its position and amplitude parameters by applying particle swarm optimization (PSO). The waveform of the extracted normal mode is simply the waveform of the source signal; the real waveform of the received normal mode can then be recovered by applying dispersion compensation to the source signal. The method presented needs only one receiver and is verified with experimental data.
In this paper, analytical expressions for the distribution of the envelope and phase of linearly modulated signals such as BPSK, M-PSK, and M-QAM in AWGN are presented. We perform numerical simulations for different orders of signal constellations. The results show that the proposed theoretical models are in excellent agreement with the estimated distributions from various numerical experiments.
17
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
In this paper, we answer the question: for any q > 0 with q ≠ 1, what are the greatest value p1= p1(q) and the least value p2= p2(q) such that the double inequality Lp1(a, b) < [L(aq, bq)]1/q < Lp2(a, b) holds for all a, b > 0 with a ≠ b? Here L(a, b) and Lp(a, b) are the logarithmic and pth generalized logarithmic means of a and b, respectively.
19
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
The concept of InterPlaNetary (IPN) Internet was proposed by National Aeronautics and Space Administration (NASA). The IPN Internet could provide Internet-like services crossing interplanetary distances in support of deep space exploration, which includes backbone network, access network, and planetary network. The IPN backbone topology control strategy based on Libration points was studied in this paper. Firstly, the location and stability of Libration point is simulated by celestial mechanics. Secondly, a novel Hierarchical-Cluster model of IPN backbone network is proposed to simplify topology design. Then Intra-Cluster Link and Inter-Cluster Link are analyzed in detail. Finally, the optimal handover moment is gotten by critical angle which to use relay theory, and the total number of handover times is calculated within a relative period between Uranus and Neptune cluster.
PL
Koncepcja interplanetarnego Internetu IPN została zaproponowana przez NASA. W artykule omówiono strategię kontroli topologii szkieletu bazującą, na punkcie Libration. Na wstępie przeanalizowano stabilność systemu a następnie model hierarchiczny klastrów. Wreszcie analizowano przełączenie połączeń między stacjami bazowymi – handover.
20
Dostęp do pełnego tekstu na zewnętrznej witrynie WWW
This paper puts forward the concept of perception technology in e-commerce and constructs synergy e-business platform through CSCW work environment to research the collaborative communication protocol and system model. Sensory information trees is constructed by the perception of synergy e-business investigation and analysis of data; establishes collaborative e-commerce structure and coordination control model of perception mechanism under the synergy e-business environmental requirements and sensory information data structure.
PL
Artykuł przedstawia założenia technologii percepcji w e-komercji. Konstruowana jest platforma synergii e-business przez uwzględnienie teorii CSCW – Computer Supported Cooperative Work.
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.