Center Of Gap Research Articles

The losses of condensed tannins in six foliar litters vary with gap position and season in an alpine forest

Condensed tannins (CTs) have been considered to be intrinsic variables that determine litter decomposition. Forest gaps and the surrounding crown canopies may locally influence the microenvironmental factors, thus affecting the losses of CTs from litter. However, little information is available about the dynamics of CTs loss in forest gaps. In this study, litterbags containing foliar litter of Minjiang fir (Abies faxoniana), red birch (Betula albosinensis), Masters larch (Larix mastersiana), cypress (Sabina saltuaria), Kangding willow (Salix paraplesia), and Lapland azalea (Rhododendron lapponicum), were placed on the forest floor at differet positions from the gap center to the closed canopy in the alpine Minjiang fir forest located in the upper reaches of the Yangtze River and the eastern Tibetan Plateau (China). The samples were retrieved during the periods of snow formation, snow cover, snow melt and in the growing season, and the CTs content was measured at each time point. During the first year, all six types of foliar litter experienced high losses of CTs with values ranging from 70.18% to 96.67%. Forest gaps accelerated litter CTs losses in the winter but inhibited CTs losses in the growing season, which demonstrated significant seasonal differences. Additionally, the litter of conifers exhibited greater CTs losses in the winter, especially during the snow formation period, whereas the litter of broadleaved trees showed greater CTs losses during the growing season. These results indicate that the predicted reductions in snow depth resulting from future winter warming and the loss of forest gaps due to forest regeneration will inhibit the decomposition of CTs in the litter of alpine forest ecosystems, which will slow soil carbon sequestration from foliar litter in cold biomes.

Nuclear signature effect on spatial distribution of molecular harmonic in the presence of spatial inhomogeneous field

Spatial distribution of the molecular harmonic spectra from in the presence of inhomogeneous field has been theoretically investigated. It shows that (i) the harmonic intensities from the negative-H nucleus play the dominating role in harmonic emission spectra. (ii) Through the investigations of the nuclear signature effect on the spatial distribution of the molecular harmonic spectra, the differences of the harmonic intensities between the negative-H nucleus and the positive-H nucleus can be enhanced and reduced with the introduction of the higher vibrational state and the heavy nucleus (i.e. ), respectively. The time-frequency analyses of the harmonic spectra, the time-dependent wave function and the electron localization have been shown to explain the harmonic spatial distribution and the electron motion. (iii) Due to the plasmon-resonance-enhancement near the metallic nanostructure, the harmonic cutoff can be remarkably enhanced as the spatial position of the inhomogeneous field moving away from the gap center. The ionization probabilities have been shown to explain the harmonic cutoff extension.

Use of a multi-level mixed methods approach to study the effectiveness of a primary care progressive return to activity protocol after acute mild traumatic brain injury/concussion in the military

The large number of U.S. service members diagnosed with concussion/mild traumatic brain injury each year underscores the necessity for clear and effective clinical guidance for managing concussion. Relevant research continues to emerge supporting a gradual return to pre-injury activity levels without aggravating symptoms; however, available guidance does not provide detailed standards for this return to activity process. To fill this gap, the Defense and Veterans Brain Injury Center released a recommendation for primary care providers detailing a step-wise return to unrestricted activity during the acute phase of concussion. This guidance was developed in collaboration with an interdisciplinary group of clinical, military, and academic subject matter experts using an evidence-based approach. Systematic evaluation of the guidance is critical to ensure positive patient outcomes, to discover barriers to implementation by providers, and to identify ways to improve the recommendation. Here we describe a multi-level, mixed-methods approach to evaluate the recommendation incorporating outcomes from both patients and providers. Procedures were developed to implement the study within complex but ecologically-valid settings at multiple military treatment facilities and operational medical units. Special consideration was given to anticipated challenges such as the frequent movement of military personnel, selection of appropriate design and measures, study implementation at multiple sites, and involvement of multiple service branches (Army, Navy, and Marine Corps). We conclude by emphasizing the need to consider contemporary approaches for evaluating the effectiveness of clinical guidance.

Growth and physiology of Hopea odorata planted within gaps in an acacia plantation acting as a nurse crop

Background: Mixtures of tropical acacia nurse crops and understorey native species have been established to aid forest restoration in Vietnam, but with partial success. Knowledge of physiological mechanisms underlying competitive interactions remains limited.Aims: To examine growth and physiological responses of Hopea odorata, a shade-tolerant dipterocarp, established within an Acacia hybrid (Acacia mangium × Acacia auriculiformis) nurse-crop plantation.Methods: H. odorata seedlings were planted within three 22-m diameter gaps in a 3-year-old Acacia hybrid plantation in Central Vietnam. Growth and physiology responses to an environmental gradient in gaps were examined over 2 years.Results: Growth rate and maximum rates of photosynthesis and stomatal conductance of H. odorata saplings increased significantly with increases in relative daily incident photosynthetically active radiation from 24% at the gap perimeter (GP) to 61% at the gap centre. Leaf N, P, and chlorophyll concentration were unaffected by position in the gap. At the end of dry season, there were significant reductions in leaf water potential for saplings close to the GP suggesting interspecific competition for water.Conclusions: Despite naturally regenerating in shade, the strong ability of H. odorata to acclimate to high light environments suggests that its re-establishment on degraded sites, using Acacia hybrid as a nurse crop should be possible, provided that competition for light and water are managed.

Simulation of Electronic Center Formation by Irradiation in Silicon Crystals

We present the results of a study on localized electronic centers formed in crystals by external influences (impurity introduction and irradiation). The main aim is to determine the nature of these centers in the forbidden gap of the energy states of the crystal lattice. For the case of semiconductors, silicon (Si) was applied as model material to determine the energy levels and concentration of radiation defects for application to both doped and other materials. This method relies on solving the appropriate equation describing the variation of the charge carrier concentration as a function of temperature n(T) for silicon crystals with two different energy levels and for a large set of N1, N2 (concentrations of electronic centers at each level), and n values. A total of almost 500 such combinations were found. For silicon, energy level values of e1 = 0.22 eV and e2 = 0.34 eV were used for the forbidden gap (with corresponding slopes determined from experimental temperature-dependent Hall-effect measurements) and compared with photoconductivity spectra. Additionally, it was shown that, for particular correlations among N1, N2, and n, curve slopes of e1/2 = 0.11 eV, e2/2 = 0.17 eV, and α = 1/2(e1 + e2) = 0.28 eV also apply. Comparison between experimental results for irradiation of silicon crystals by 3.5-MeV energy electrons and Co60γ-quanta revealed that the n(T) curve slopes do not always coincide with the actual energy levels (electronic centers).

High-order harmonic emission in bowtie-shaped nanostructure with few-cycle spatially inhomogeneous laser fields when the atom is placed at different spatial positions

In this study, we investigate the harmonic spectra in the vicinity of the center of the nanostructure gap when helium atom is placed at different spatial positions. We find that the high-order harmonic spectra is very sensitive to the atomic spatial positions in a inhomogeneous laser field. When the initial atomic spatial position is changed from −9.0 a.u. to 9.0 a.u., the cutoff of the high-order harmonic generation (HHG) can be extended, and the supercontinuum harmonic spectrum of the second plateau is extended to the high-order and the low-order simultaneously. The HHG process is demonstrated by using the time-frequency analysis, the semi-classical three-step model and the ionization probability.

Systematic First-Principles Calculations of Charge Transfer Transitions of Transition Metal Ions in α-Al2O3 and Optimization of the Computational Condition

[Introduction] Persistent phosphors are materials showing continuous luminescence for long durations from several minutes to hours after optical excitation has ceased. The materials have carrier traps that play the most important role in the persistent luminescence process. Ueda et al. of Kyoto University developed a blue-light-induced persistent luminescence material Ce3+ -Cr3+:Y3Al2Ga3O12 by doping Cr into Ce3+:Y3Al2Ga3O12, where the 3d orbitals of Cr3+ work as trap centers to capture electrons[1]. The persistent luminescence properties are dominated by the position of the energy levels of the trap centers in the band gap and therefore can be controlled by changing the doped transition metal (TM) ion. Generally, it is difficult to calculate the band gap energy by first-principles calculations based on the cluster method due to the poor reproduction of the conduction band. Accordingly, the transition energy from the impurity level to the conduction band cannot be calculated directly. However, the position of the impurity level within the band gap can be estimated by calculating the charge transfer transition energy from the valence band (Ligand to Metal Charge Transfer: LMCT). In this study, in order to obtain the LMCT energy for various trivalent TM ions in α-Al2O3, we performed first-principles calculations using the DVME method[2]based on configuration interaction (CI) method and constructed the theoretical energy diagram of the transition metal 3d levels within the band gap. By comparing the theoretical diagram with the available experimental LMCT energies in detail, the optimized computational condition was also proposed. [Computational Method] We constructed a 7-atom cluster with C3 symmetry consisting of the central aluminum ion and the first-neighbor oxygen ions from the crystal data of α-Al2O3 [3]and then we substituted various trivalent TM (Sc, Ti, V, Cr, Mn, Fe, Co) ions for the central aluminum ion. The effective Madelung potential was considered by setting point charges on the atomic sites around the cluster. In order to improve the computational accuracy, the lattice relaxation (LR) caused by the substitution of TM for aluminum was considered by estimating the change of the bond length based on the Shannon’s crystal radii, and the configuration dependent correction (CDC) was also considered. The LMCT energy was calculated as the transition energy from the top of the valence band corresponding to the highest one of the MOs mainly consisting of oxygen 2p orbital to the MO mainly consisting of TM 3d orbital based on the MO calculation using the DV-Xα method and the CI calculation using the DVME method. [Result] The theoretical LMCT energies calculated with LR and CDC are shown as the diagram in Fig. 1 together with the diagram for the experimental values[4-6]. The figure shows that the experimental trend was successfully reproduced by first-principles calculations. The remaining underestimation for Sc and Ti is probably due to the overestimation of the lattice relaxation arising from the simple approximation. On the other hand, the overestimation for Fe is probably due to the insufficient consideration of electron correlation. [References] [1] J. Ueda, et al,. Appl. Phys. Lett. 104, 101904, (2014). [2] K. Ogasawara, et al., Phys. Rev. B, 64, 115413, (2001). [3] E. N. Maslen, et al., Acta Crystallogr. Sect. B, 49, 973-980 (1993). [4] B. R. Namozov, et al., Physics of the Solid State, 40, 599-600 (1998). [5] H. H. Tippins, Phys. Rev. B, 1, 126-135 (1970). [6] D. S. McClure, J. Phys. Chem., 36, 2757-2779 (1962). Figure 1

Influence of canopy gaps on saproxylic beetles in primeval beech forests: a case study from the Uholka‐Shyrokyi Luh forest, Ukraine

Abstract The distribution of canopy gaps has been studied intensively in primeval forest, but their role as keystone structure for biodiversity under natural conditions is still poorly understood. We investigated the effect of habitat properties on saproxylic beetles in the centre, at the edge of gaps and in closed stands in one of the last and largest primeval beech forest of Europe (Uholka‐Shyrokyi Luh forest, Ukraine). The abundance of saproxylic beetles was significantly higher in canopy gaps compared to the closed forest. The number of species did not differ significantly between gap centres and closed forest, but was higher in gap centres than at gap edges. Species composition in gap centres was clearly distinct from that in closed forests. The effects of biotic resources, such as the amount of dead wood or the density of big trees (DBH>70 cm), on diversity measures were weak, which might be caused by the abundance of these resources under natural conditions. Since our study site is embedded in a landscape dominated by primeval forest, the effects of habitat properties on saproxylic beetle fauna might differ from that in managed forests of Central Europe. Nevertheless, species assemblages in primeval beech forests play an important role as a reference for conservation efforts in managed beech forests of Europe.

Transitions between various diffuse discharge modes in atmospheric-pressure helium in the medium-frequency range

In this paper, we investigate DBDs in the medium frequency range (MF, 0.3–3 MHz). More precisely, for a 2 inter-dielectric gap in helium at atmospheric pressure, the frequency is varied from 1.0 to 2.7 MHz. The generated discharge shows similarities with both the low-frequency atmospheric-pressure glow discharge (APGD) and the atmospheric pressure capacitively coupled radio-frequency (CCRF) discharge. In the frequency range under investigation, two diffuse discharge modes can be observed depending on the voltage applied between the electrodes. At low applied voltage, the discharge emissions are barely visible and are concentrated in the center of the gas gap similarly to CCRF discharges in the mode where the electron density is concentrated in the bulk. Ohmic heating is the main power transfer mechanism. At higher applied voltage, the discharge emissions are 10 times more intense and are closer to the dielectric surfaces similarly to the more common radio-frequency α mode. These two discharge modes can be observed in the same experimental conditions with the amplitude of the applied voltage as sole control parameter. The gas temperature obtained from N2 impurities rotational spectrum increases from room temperature to about 500 K while the power density rises from 10−1 to 101 W cm−3 when the applied voltage is increased. In addition, when the discharge transits back and forth from the to the α mode, a hysteresis is observed. The transition from the to the α mode occurs abruptly with a large RMS current increase while the transition from the α to the mode is rather smooth with no significant discontinuity in the RMS current.

Making up for lost time: Biophysical constraints on the temporal abundance of two fiddler crabs in wet-dry tropical mangroves

Biophysical models are used to predict the spatial distributions of organisms. Nevertheless, understanding factors influencing the temporal distributions of animals may often be additionally required. It is expected that intertidal macrofauna of the wet–dry tropics face a multitude of temporal challenges because there is not only seasonal drying but also variation in surface moisture over the circatidal cycle. Activities of fiddler crabs (Uca spp.) depend on adequate surface moisture being available for feeding and respiration. A recent study monitored crab abundance during spring tides and found that one Uca species in the mangroves of Darwin Harbour, Australia, U. flammula, is most abundant in the wet season, while another, U. elegans, is most abundant in the dry season. We hypothesized here that these seemingly contradictory abundance patterns are driven by temporal variation in the availability of soil moisture within each species habitat. We thus monitored crab abundance and measured soil moisture content across four types of habitat (low gap centres, low gap edges, mid-height gap centres and high gap centres) seasonally and across the circatidal cycle. We found that crab abundance and soil moisture both varied over time among habitat types. We used a log-linear model to show that habitat type influenced soil moisture and this in turn influenced crab abundance. Sampling across the circatidal cycle showed that U. flammula was more abundant in the wet season, as reported previously, while the abundance of U. elegans did not vary between seasons. Our model suggested that U. elegans ‘makes up for lost time’ in the dry season by undertaking all activities during spring tide low water as only at this time is the substratum moist enough for feeding and respiration. We highlight the importance of measuring multiple variables across habitats over small and large scales when assessing temporal abundance patterns of intertidal tropical organisms.

Structural, electronic and optical properties of B, N and Ni-doped zinc-blende GeC by first-principles calculation

The structural, electronic and optical properties of intrinsic and doped (B, N, and Ni) zinc-blende germanium carbide (ZB-GeC) are investigated by the first-principles calculation. The results show that substitution of B, Ni in Ge sub-lattice site and N in C sub-lattice site are energetically more favorable. The band structures of B- and N-doped ZB-GeC show p- and n-type semiconductor characteristic, respectively. While for Ni-doped ZB-GeC, new dopant-induced energy levels emerge in the center of the band gap. Indirect to direct transition and gap shrink occur when the dopants are incorporated. Furthermore, Ni-doped ZB-GeC is found to be a paramagnetic material. The imaginary parts of dielectric functions reveal that the doping can improve the photo-absorption efficiency of ZB-GeC with new absorbing peaks emerge in the near-infrared region, visible region, and middle-ultraviolet region in the absorption spectrum. The conductivity spectra of doped ZB-GeC shows that the conductivity of ZB-GeC also gets improved. These features indicate that the doped ZB-GeC can be a promising optoelectronic material.

Mechanism of VHF H2 plasma production at high pressures

A VHF H2 plasma was produced by a narrow-gap discharge at high pressures, and the plasma parameters were examined with the Langmuir probe. A bi-Maxwellian electron distribution was observed near the discharge electrode at a discharge gap of 10 mm, while a Maxwellian distribution was seen near the center. When the discharge gap was 15 mm, electrons had a Maxwellian distribution independent of the position. It was found that there must be a threshold in the discharge gap for stochastic heating to occur. The plasma potential near the discharge electrode was higher than that near the center of the interelectrode gap, suggesting the existence of negative ions. The simulation using the plasma hybrid code was carried out. The spatial profiles of the density and temperature of electrons were similar to the experimental results. The plasma potential had a hill-like profile that was quite different from the measured one. The negative ion density was negligible.

Plasmon transmission through excitonic subwavelength gaps.

We study the transfer of electromagnetic energy across a subwavelength gap separating two co-axial metal nanorods. In the absence of spacer in the gap separating the rods, the system exhibits strong coupling behavior between longitudinal plasmons in the two rods. The nature and magnitude of this coupling are studied by varying various geometrical parameters. As a function of frequency, the transmission is dominated by a split longitudinal plasmon peak. The two hybrid modes are the dipole-like "bonding" mode characterized by a peak intensity in the gap and a quadrupole-like "antibonding" mode whose amplitude vanishes at the gap center. When the length of one rod is varied, this mode spectrum exhibits the familiar anti-crossing behavior that depends on the coupling strength determined by the gap width. When off-resonant 2-level emitters are placed in the gap, almost no effect on the frequency dependent transmission is observed. In contrast, when the molecular system is resonant with the plasmonic line shape, the transmission is strongly modified, showing characteristics of strong exciton-plasmon coupling. Most strongly modified is the transmission near the lower frequency "bonding" plasmon mode. The presence of resonant molecules in the gap affects not only the molecule-field interaction but also the spatial distribution of the field intensity and the electromagnetic energy flux across the junction.

Engineering Band Edge Positions of Nickel Oxyhydroxide through Facet Selection

A promising material for catalysis should have appropriate band edge positions. Unfortunately, the band edge positions are unknown for nickel oxyhydroxide (NiOOH), one of the best water oxidation catalysts. We present here first-principles calculations of band edge positions for surfaces of pure NiOOH. Specifically, the band edge positions of NiOOH (001), (100), and (015) were calculated using density functional theory (DFT) + U, PBE0, and G0W0 methods by using slab models for the surfaces with a vacuum region and periodic boundary conditions. The band edge positions were determined by calculating the band gap center using DFT + U and by accounting for the band gap using G0W0. This approach was validated with other methods. Our results show that due to the polarity of NiOOH, the valence band position is especially sensitive to surface orientation: facets with O–H bonds parallel to the normal of the surface have the highest valence band edge. The following relation between valence band edges is obtained: ...

Colored Diffuse Mini Jets in Runaway Electrons Preionized Diffuse Discharges

Optical emission of the nanosecond diffuse discharge initiated by runaway electrons in an inhomogeneous electric field was investigated in a single-pulse and pulse-periodic modes in different gases (air, nitrogen, and argon). The amplitude of voltage pulses, pulse rise time, and interelectrode distance were, respectively, 200 kV, 0.5 ns, and 13 mm for single-pulse mode, and 13 kV, 4 ns, and 2 mm for pulse-periodic mode. In the single-pulse mode, the diffuse mini jets (DMJs) of different colors with lengths up to 7 mm appear near electrodes. Blue DMJs were observed near electrodes with a small radius of curvature made of a stainless steel. Red DMJs were observed near the grounded flat electrode made of aluminum and in the center of discharge gap near a spark channel. It was shown that radiation intensity of DMJs increased with the increase in nitrogen pressure up to 0.4 MPa, but subsequent increase in pressure up to 0.7 MPa led to the decrease in radiation intensity. In the pulse-periodic mode, colored DMJs are observed as well, the size of which was $\sim 1$ mm. In this mode, the spectral and amplitude-temporal parameters of the radiation of DMJs have been studied. It was shown that the color of DMJs is determined by the radiation of electrode metal vapors. It was shown that the DMJs originate from the bright spots (explosive centers) on electrodes.

Gap locations influence the release of carbon, nitrogen and phosphorus in two shrub foliar litter in an alpine fir forest.

Gap formation favors the growth of understory plants and affects the decomposition process of plant debris inside and outside of gaps. Little information is available regarding how bioelement release from shrub litter is affected by gap formation during critical periods. The release of carbon (C), nitrogen (N), and phosphorus (P) in the foliar litter of Fargesia nitida and Salix paraplesia in response to gap locations was determined in an alpine forest of the eastern Qinghai-Tibet Plateau via a 2-year litter decomposition experiment. The daily release rates of C, N, and P increased from the closed canopy to the gap centers during the two winters, the two later growing seasons and the entire 2 years, whereas this trend was reversed during the two early growing seasons. The pairwise ratios among C, N, and P converged as the litter decomposition proceeded. Compared with the closed canopy, the gap centers displayed higher C:P and N:P ratio but a lower C:N ratio as the decomposition proceeded. Alpine forest gaps accelerate the release of C, N, and P in decomposing shrub litter, implying that reduced snow cover resulting from vanishing gaps may inhibit the release of these elements in alpine forests.

AC electric field induced dielectrophoretic assembly behavior of gold nanoparticles in a wide frequency range

In this work, we focus on frequency-dependence of pearl chain formations (PCF) of gold nanoparticles driven by AC dielectrophoresis (DEP), especially in a low field-frequency range, where induced double-layer charging effect at ideally polarizable surfaces on particle DEP behavior and surrounding liquid motion need not be negligible. As field frequency varies, grown features of DEP assembly structures ranging from low-frequency non-bridged gap to high-frequency single gold nanoparticle-made nanowires bridging the electrodes are demonstrated experimentally. Specifically, at 10kHz, a kind of novel channel-like structure with parallel opposing banks is formed at the center of interelectrode gap. In stark contrast, at 1MHz, thin PCF with diameter of 100nm is created along the shortest distance of the isolation spacing. Moreover, a particular conductive path of nanoparticle chains is produced at 1MHz in a DEP device embedded with multiple floating electrodes. A theoretical framework taking into account field-induced double-layer polarization at both the particle/electrolyte and electrode/electrolyte interface is developed to correlate these experimental observations with induced-charge electrokinetic (ICEK) phenomenon. And a RC circuit model is helpful in accounting for the formation of this particular non-bridged channel-like structure induced by a low-frequency AC voltage. As compared to thin PCF formed at high field frequency that effectively short circuits the electrode pair, though it is difficult for complete PCF bridging to occur at low frequency, the non-bridged conducting microstructure has potential to further miniaturize the size of electrode gap fabricated by standard micromachining process and may find useful application in biochemical sensing.

Establishment of invasive plant species in canopy gaps on Robinson Crusoe Island

To design preventive and management measures it is crucial to identify the mechanisms that facilitate an invasion process. We evaluated how microsites affect establishment success of the alien small tree Aristotelia chilensis, the alien climber Rubus ulmifolius, and endemic tree species on Robinson Crusoe Island forest. Seedling and sapling densities were estimated in 65 canopy gaps in two forest stands (PEY and Villagra) along a canopy forest-gap gradient, and in three microsites (mound, pit, and trunk) of canopy gap-maker trees. Two statistical models were applied to evaluate the effects of the position in the gap (center, edge, and close forest) and substrate microsites in relation to topographic and structural variables on invasive and endemic species establishment. The density of invasive species was higher in the center of canopy gaps and forest edges than under forest canopy. Invasive plants were present in 86.5 % (n = 32 gaps in PEY) and 89.8 % (n = 25 forest gaps) in Villagra. A higher seedling and sapling density of endemic rather than invasive species was found in canopy-gap center and gap edges. However, trunks, mounds, and pits were dominated by invasive species. We found different responses in seedlings, saplings, and juvenile stages in relation to the explanatory variables studied and between the two stands. The decomposition state of gap-maker trees, which was used as a proxy of gap age, was the only variable that showed the same tendency in the two forest stands and for both invasive and endemic seedlings. In this case, we found that the densities of invasive and endemic seedlings were lower in older gaps, but sapling densities were higher in older gaps. Based on the results we cannot conclude a general pattern of seedling, sapling, and juvenile establishment in forest gaps for either invasive species, but in some gaps the invasion seems to start in trunks, mounds, and pits. We recommend focusing invasive species control on mounds and pits in some forest stands; and in general, we recommend controlling invasive saplings, more than seedlings or juveniles.

Structural, optical, transient photoconductivity studies and low temperature thermoelectric power measurements on reactively evaporated lead selenide thin films

Thin film of PbSe has been prepared on ultrasonically cleaned glass substrate at a substrate temperature of 373 ± 5 K by reactive evaporation at a pressure of 10−5 mbar. The prepared PbSe film is characterized using X-ray diffraction, scanning electron microscopy, and UV–Vis–NIR spectrophotometer. The average particle size, number of crystallite per unit area and strain of a typical film are calculated and found as 38 nm, 3.098 × 1015 m−2 and 2.253 × 10−3 respectively. The room temperature electrical resistivity of the film is of the order of 0.16 Ω cm. The material possesses a direct allowed optical band gap of 2.02 eV and the absorption coefficient is found to be in the range 104–105 cm−1. The weak absorption below the absorption band edge is observed and tailing in the forbidden gap is found to follow Urbach tail rule. The width of the localized states in the band gap is estimated as 256 meV. The differential life time increases with increasing decay time and the decay curve of the photocurrent gives the localized energy states which act as trapping centre in the band gap of the material. The thermoelectric power measurements are done in the temperature range 10–293 K and the Fermi level is positioned at 0.039 eV above the valence band. The material possesses a Seebeck coefficient of about 137 μV K−1 and power factor of 0.12 × 10−4 Wm−1 K−2 near room temperature. The prepared films are of p-type in nature with activation energy of 0.063 eV.

Forest Gaps Alter the Total Phenol Dynamics in Decomposing Litter in an Alpine Fir Forest.

The total phenol content in decomposing litter not only acts as a crucial litter quality indicator, but is also closely related to litter humification due to its tight absorption to clay particles. However, limited attention has been focused on the total phenol dynamics in foliar litter in relation to forest gaps. Here, the foliar litter of six representative tree species was incubated on the forest floor from the gap center to the closed canopy of an alpine Minjiang fir (Abies faxoniana) forest in the upper reaches of the Yangtze River and eastern Tibetan Plateau. The dynamics of total phenol concentration in the incubated litter was measured from November 2012 to October 2014. Over two-year incubation, 78.22% to 94.06% of total phenols were lost from the foliar litter, but 52.08% to 86.41% of this occurred in the first year. Forest gaps accelerated the loss of total phenols in the foliar litter in the winter, although they inhibited the loss of total phenols during the growing season in the first year. In comparison with the effects of forest gaps, the variations of litter quality among different species were much stronger on the dynamics of total phenols in the second year. Overall, the loss of total phenols in the foliar litter was slightly higher in both the canopy gap and the expanded gap than in the gap center and under the closed canopy. The results suggest that the predicted decline in snow cover resulting from winter warming or vanishing gaps caused by forest regeneration will retard the loss of total phenol content in the foliar litter of alpine forest ecosystems, especially in the first decomposition year.