Spatial pattern dynamics among co-dominant populations in early secondary forests in Southwest China

The canopy of subtropical natural forests usually consists of several co-dominant populations(CDPs),which play a crucial role in forest structure,formation of the forest environment,and ecological function.However,little attention has been given to changes in spatial patterns in CDPs during natural succession.Cyclobalanopsis glauca(Thunb.)Oerst.,Quercus variabilis Blume,and Pinus yunnanensis var.tenuifolia W.C.Cheng & Y.W.Law are canopy species that form CDPs in zonal forests along the Nanpan River in southwest China.We used the g(r) function and its bivariate distribution model,g_(12)(r),which is based on distances between pairs of points,to explore the dynamics of the three CDP species with respect to distribution patterns and spatial correlations in two secondary forests(one 30-year-old forest [30-YF] and one 57-year-old forest [57-YF]).The following key results were obtained:(1) there was a clumped pattern in the 30-YF,but the intensity of aggregation varied among populations and life stages.The distribution pattern gradually shifted to become random with longer succes sion time(i.e.,30-YF vs.57-YF),expansion of the observation scale(r=0-20 m),and at later life stages.(2) Aside from the mid-sized C.glauca trees and large P.yunnanensis trees,the trees repulsed each other at certain scales(r=0-2,5-6,11-12,14-16 m) in the 30-YF.Almost all of the life stages in the CDPs were independently correlated.This independent correlation was exacerbated by a longer succession time.(3) An increase in life stages and longer succession also promoted independent changes in intraspecific correlations.(4) Intraspecific correlations were stronger than interspecific correlations.Our results showed that reducing exclusive competition is essential to coexistence in CDPs.Inter-and intra-specific repulsion may occur at the same time,but intraspecific repulsion was the main driving force behind the random distributions and independent correlations.

Global woodland structure from local interactions:new nearest-neighbour functions for understanding the ontogenesis of global forest structure

Background:A number of hypotheses and theories,such as the Janzen-Connell hypothesis,have been proposed to explain the natural maintenance of biodiversity in tropical and temperate forest ecosystems.However,to date the details of the processes behind this natural maintenance are still unclear.Recently two new nearest-neighbour characteristics were proposed and in this paper we demonstrate how they can contribute to a better understanding of the ontogenesis of global forest structure from localised neighbourhoods.Methods:We applied the new species and size segregation functions together with appropriate test procedures to four example woodland data sets from China at Daqingshan,Jiaohe,Jiulongshan and Xiaolongshan forest regions.In addition we quantified the morphology of the new characteristics and modelled a neighbourhood allometric coefficient linking the two functions.Results:The results revealed quite different species segregation patterns with both conspecific and heterospecific attraction.We found these to be generally matched by equivalent size segregation patterns of attraction of similar and different sizes.It was straightforward to model the size segregation function from the knowledge of the species segregation function by estimating a neighbourhood allometric coefficient.Conclusions:The new characteristics have helped to quantify the extent and rate of decline of neighbourhood interactions in terms of spatial species and size diversity.Through the allometric neighbourhood coefficient the analysis highlighted once more how closely related species and size segregation are,thus supporting the minglingsize hypothesis.Using both a traditional and a restricted random-labelling test has provided a valuable tool for understanding the exact nature of species-mingling and size-inequality relationships.

Machining Deformation Prediction of Thin-Walled Part Based on Finite Element Analysis

For the problems of machining distortion and the low accepted product during milling process of aluminum alloy thin-walled part,this paper starts from the analysis of initial stress state in material preparation process,the change process of residual stress within aluminum alloy pre-stretching plate is researched,and the distribution law of residual stress is indirectly obtained by delamination measurement methods,so the effect of internal residual stress on machining distortion is considered before finite element simulation. Considering the coupling effects of residual stress,dynamic milling force and clamping force on machining distortion,a threedimensional dynamic finite element simulation model is established,and the whole cutting process is simulated from the blank material to finished product,a novel prediction method is proposed,which can availably predict the machining distortion accurately. The machining distortion state of the thin-walled part is achieved at different processing steps,the machining distortion of the thin-walled part is detected with three coordinate measuring machine tools,show that the simulation results are in good agreement with experimental data.

Discussion about the Relationship between Thunderstorm Days and Lightning Density

[Objective]The study aimed to discuss the relationship between thunderstorm days and lightning density. [Method]Based on the data of lightning density and thunderstorm days in Dalian region from 2007 to 2011,the optimal radius for the assessment of lightning risk was determined firstly,and then the relationship between thunderstorm days and lightning density in Dalian was fitted using the least square method. [Result]The optimal radius for the assessment of lightning risk was 25 km. The relation between lightning density and thunderstorm days could be fitted well by the formula y =0. 091x2-3. 447 2x ＋34. 713. [Conclusion]The fitting result was consistent with the actual situation,so the formula can be used in relative studies of Dalian.

Multi-channel phase regeneration of QPSK signals based on phase sensitive amplification

In this paper,we propose and demonstrate simultaneous phase regeneration of four different channels of QPSK signal based on phase sensitive amplification.The configuration can be divided into two parts.The first one uses four wave mixing in high nonlinear fiber(HNLF)to generate the corresponding three harmonic conjugates precisely at the frequency of the original signals.The other one uses optical combiner to realize coherent addition which is aimed at completely removing the interaction in phase regeneration stage.The simulation results suggest that this scheme can optimize signal constellation to a large extend especially in high noise environment.Besides,optical signal to noise ratio(OSNR)can improve more than 3 dB while the bit-error-rate(BER)reaches 10 – 3 with a constant white noise and 15° phase noise.

Synthesis of titanium carbide coating on Ti15Mo alloy and its tribological behaviour

Ti15Mo alloy has been regarded as one of the most potential biomedical materials due to its excellent performance.However,the low hardness and poor wear resistance of titanium alloy limit the further application.Therefore,high temperature solid carburising technology was performed on the surface of Ti15Mo alloys to prepare titanium carbide(TiC)coating with graphene(G)as the carburising agent.The microstructure,mechanical properties,and tribological properties of TiC coating under different lubricants were investigated.Results showed that TiC coating was closely bonded to the titanium substrate.The maximum thickness of TiC coating treated with 1150°C was approximately 184.02μm,and the microhardness of alloys treated with 1100°C can achieve 1221.5 HV.All modified Ti15Mo alloys showed improved tribological performance compared to the original samples.The wear mechanisms of modified Ti15Mo alloys were abrasive wear and adhesive wear under the SBF lubricant,and the TiC coating was slightly peeled off.The overall friction coefficient and wear rate under 25%calf serum lubricant were lower than the SBF lubricant,and surface scratches were almost absent,and slight abrasive wear and adhesive wear occurred on the surface.

FOXO1-miR-506 axis promotes chemosensitivity to temozolomide and suppresses invasiveness in glioblastoma through a feedback loop of FOXO1/miR-506/ETS1/FOXO1

To explore the role of forkhead box protein O1(FOXO1)in the progression of glioblastoma multiforme(GBM)and related drug resistance,we deciphered the roles of FOXO1 and miR-506 in proliferation,apoptosis,migration,invasion,autophagy,and temozolomide(TMZ)sensitivity in the U251 cell line using in vitro and in vivo experiments.Cell viability was tested by a cell counting kit-8(CCK8)kit;migration and invasion were checked by the scratching assay;apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling(TUNEL)staining and flow cytometry.The construction of plasmids and dual-luciferase reporter experiment were carried out to find the interaction site between FOXO1 and miR-506.Immunohistochemistry was done to check the protein level in tumors after the in vivo experiment.We found that the FOXO1-miR-506 axis suppresses GBM cell invasion and migration and promotes GBM chemosensitivity to TMZ,which was mediated by autophagy.FOXO1 upregulates miR-506 by binding to its promoter to enhance transcriptional activation.MiR-506 could downregulate E26 transformation-specific 1(ETS1)expression by targeting its 3'-untranslated region(UTR).Interestingly,ETS1 promoted FOXO1 translocation from the nucleus to the cytosol and further suppressed the FOXO1-miR-506 axis in GBM cells.Consistently,both miR-506 inhibition and ETS1 overexpression could rescue FOXO1 overactivation-mediated TMZ chemosensitivity in mouse models.Our study demonstrated a negative feedback loop of FOXO1/miR-506/ETS1/FOXO1 in GBM in regulating invasiveness and chemosensitivity.Thus,the above axis might be a promising therapeutic target for GBM.

Tribo-corrosion mechanisms and electromechanical behaviours for metal implants materials of CoCrMo,Ti6Al4V and Ti15Mo alloys

Corrosion and wear play significant roles in the aseptic loosening of artificial hip joints for the long-term service.In this present study,tribo-corrosion tests were carried out through a reciprocating ball-on-plate system to evaluate the corrosion and wear prop-erties of CoCrMo,Ti6Al4V and Ti15Mo alloys in a simulated body fluid(SBF)solution.It was found that the tribo-corrosion behaviours of CoCrMo/Al_(2)O_(3)and Ti15Mo/Al_(2)O_(3)systems had significant wear-corrosion synergistic interaction,and wear-induced corro-sion was dominant.For Ti6Al4V/Al_(2)O_(3)systems,their wear mechanism under SBF lubrication was a combination of abrasive,adhesive and fatigue wear.While the wear mechanism of the Ti15Mo/Al_(2)O_(3)system under synergistic interaction was a combination of abrasive and adhesive wear.Finally,it was suggested that the Ti15Mo alloy would be the better alternative for metal implant applications compared with the CoCrMo alloy for the consideration of both wear and potential poisonous ions such as Co(III)and Cr(VI).