Tree mortality, fire scar formation and regeneration 8 years after low-intensity fire in managed Pinus sylvestris stands

Fire is an important driver of the boreal forest ecosystem, and a useful tool for the restoration of degraded forests. However, we lack knowledge on the ecological processes initiated by prescribed fires, and whether they bring about the desired restoration effects. The purpose of this study was to investigate the impacts of low-intensity experimental prescribed fires on four ecological processes in young commercial Scots pine (Pinus sylvestris) stands eight years after the burning. The processes of interest were tree mortality, dead wood creation, regeneration and fire scar formation. These were inventoried in twelve study plots, which were 30 m x 30 m in size. The plots belonged to two different stand age classes: 30-35 years or 45 years old at the time of burning. The study was partly a follow-up of study plots researched by Sidoroff et al. (2007) one year after burning in 2003. Tree mortality increased from 183 stems ha-1 in 2003 to 259 stems ha-1 in 2010, corresponding to 15 % and 21 % of stem number respectively. Most mortality was experienced in the stands of the younger age class, in smaller diameter classes and among species other than Scots pine. By 2010, the average mortality of Scots pine per plot was 18%, but varied greatly ranging from 0% to 63% of stem number. Delayed mortality, i.e. mortality that occurred between 2 and 8 years after fire, seemed to become more important with increasing diameter. The input of dead wood also varied greatly between plots, from none to 72 m3 ha-1, averaging at 12 m3 ha-1. The amount of fire scarred trees per plot ranged from none to 20 %. Four out of twelve plots (43 %) did not have any fire scars. Scars were on average small: 95% of scars were less than 4 cm in width, and 75% less than 40 cm in length. Owing to the light nature of the fire, the remaining overstorey and thick organic layer, regeneration was poor overall. The abundance of pine and other seedlings indicated a viable seed source existed, but the seedlings failed to establish under dense canopy. The number of saplings ranged from 0 to 12 333 stems ha-1. The results of this study indicate that a low intensity fire does not necessarily initiate the ecological processes of tree mortality, dead wood creation and regeneration in the desired scale. Fire scars, which form the basis of fire dating in fire history studies, did not form in all cases.

Temperature-dependent chirped coherent phonon dynamics in Bi2Te3 using high-intensity femtosecond laser pulses

Degenerate pump-probe reflectivity experiments have been performed on a single crystal of bismuth telluride (Bi2Te3) as a function of sample temperature (3 K to 296 K) and pump intensity using similar to 50 femtosecond laser pulses with central photon energy of 1.57 eV. The time-resolved reflectivity data show two coherently generated totally symmetric A(1g) modes at 1.85 THz and 3.6 THz at 296 K which blue-shift to 1.9 THz and 4.02 THz, respectively, at 3 K. At high photoexcited carrier density of similar to 1.7 x 10(21) cm(-3), the phonon mode at 4.02 THz is two orders of magnitude higher positively chirped (i.e the phonon time period decreases with increasing delay time between the pump and the probe pulses) than the lower-frequency mode at 1.9 THz. The chirp parameter, beta is shown to be inversely varying with temperature. The time evolution of these modes is studied using continuous-wavelet transform of the time-resolved reflectivity data. Copyright (C) EPLA, 2010

Propagating intensity disturbances in polar corona as seen from AIA/SDO

Context. Polar corona is often explored to find the energy source for the acceleration of the fast solar wind. Earlier observations show omni-presence of quasi-periodic disturbances, traveling outward, which is believed to be caused by the ubiquitous presence of outward propagating waves. These waves, mostly of compressional type, might provide the additional momentum and heat required for the fast solar wind acceleration. It has been conjectured that these disturbances are not due to waves but high speed plasma outflows, which are difficult to distinguish using the current available techniques. Aims. With the unprecedented high spatial and temporal resolution of AIA/SDO, we search for these quasi-periodic disturbances in both plume and interplume regions of the polar corona. We investigate their nature of propagation and search for a plausible interpretation. We also aim to study their multi-thermal nature by using three different coronal passbands of AIA. Methods. We chose several clean plume and interplume structures and studied the time evolution of specific channels by making artificial slits along them. Taking the average across the slits, space-time maps are constructed and then filtration techniques are applied to amplify the low-amplitude oscillations. To suppress the effect of fainter jets, we chose wider slits than usual. Results. In almost all the locations chosen, in both plume and interplume regions we find the presence of propagating quasi-periodic disturbances, of periodicities ranging from 10-30 min. These are clearly seen in two channels and in a few cases out to very large distances (approximate to 250 `') off-limb, almost to the edge of the AIA field of view. The propagation speeds are in the range of 100-170 km s(-1). The average speeds are different for different passbands and higher in interplume regions. Conclusions. Propagating disturbances are observed, even after removing the effects of jets and are insensitive to changes in slit width. This indicates that a coherent mechanism is involved. In addition, the observed propagation speed varies between the different passpands, implying that these quasi-periodic intensity disturbances are possibly due to magneto-acoustic waves. The propagation speeds in interplume region are higher than in the plume region.

Critical stress intensity factors for cracked hollow pipes under transient thermal loads

Finite element analyses of a long hollow cylinder having an axisymmetric circumferential internal edge crack, subjected to convective cooling on the inner surface are performed. The transient thermal stress intensity factor is estimated using a domain version of the J-integral method. The effect of the thickness of the cylinder, crack length, and heat transfer coefficient on the stress intensity factor history are studied. The variations of critical normalized stress intensity factor with crack length-to-thickness ratio for different parameters are presented. The results show that if a small inner surface crack begins to grow, its stress intensity factor will increase with increase in crack length, reach a maximum, and then begin to drop. Based on the results, a fracture-based design methodology for cracked hollow pipes under transient thermal loads is discussed.

Investigation of short-time isomerization dynamics in p-nitroazobenzene from resonance Raman intensity analysis

Resonance Raman (RR) spectra are presented for p-nitroazobenzene dissolved in chloroform using 18 excitation Wavelengths, covering the region of (1)(n --> pi*) electronic transition. Raman intensities are observed for various totally symmetric fundamentals, namely, C-C, C-N, N=N, and N-O stretching vibrations, indicating that upon photoexcitation the excited-state evolution occurs along all of these vibrational coordinates. For a few fundamentals, interestingly, in p-nitroazobenzene, it is observed that the RR intensities decrease near the maxima of the resonant electronic (1)(n --> pi*) transition. This is attributed to the interference from preresonant scattering due to the strongly allowed (1)(pi --> pi*) electronic transition. The electronic absorption spectrum and the absolute Raman cross section for the nine Franck-Condon active fundamentals of p-nitroazobenzene have been successfully modeled using Heller's time-dependent formalism for Raman scattering. This employs harmonic description of the lowest energy (1)(n --> pi*) potential energy surface. The short-time isomerization dynamics is then examined from a priori knowledge of the ground-state normal mode descriptions of p-nitroazobenzene to convert the wave packet motion in dimensionless normal coordinates to internal coordinates. It is observed that within 20 fs after photoexcitation in p-nitroazobenzene, the N=N and C-N stretching vibrations undergo significant changes and the unsubstituted phenyl ring and the nitro stretching vibrations are also distorted considerably.

Studies on a new high-intensity low-emission burner

This paper presents computational and experimental results on a new burner configuration with a mild combustion concept with heat release rates up to 10 MW/m(3). The burner configuration is shown to achieve mild combustion by using air at ambient temperature at high recirculation rates (similar to250%-290%) both experimentally and computationally. The principal features of the configuration are: (1) a burner with forward exit for exhaust gases; (2) injection of gaseous fuel and air as multiple, alternate, peripheral highspeed jets at the bottom at ambient temperature, thus creating high enough recirculation rates of the hot combustion products into fresh incoming reactants; and (3) use of a suitable geometric artifice-a frustum of a cone to help recirculation. The computational studies have been used to reveal the details of the flow and to optimize the combustor geometry based on recirculation rates. Measures, involving root mean square temperature fluctuations, distribution of temperature and oxidizer concentration inside the proposed burner, and a classical turbulent diffusion jet flame, are used to distinguish between them quantitatively. The system, operated at heat release rates of 2 to 10 MW/m(3) (compared to 0.02 to 0.32 MW/m(3) in the earlier studies), shows a 10-15 dB reduction in noise in the mild combustion mode compared to a simple open-top burner and exhaust NOx emission below 10 ppm for a 3 kW burner with 10% excess air. The peak temperature is measured around 1750 K, approximately 300 K lower than the peak temperature in a conventional burner.

Thermal Weight Functions and Stress Intensity Factors for Bonded Dissimilar Media Using Body Analogy

In this study, an analytical method is presented for the computation of thermal weight functions in two dimensional bi-material elastic bodies containing a crack at the interface and subjected to thermal loads using body analogy method. The thermal weight functions are derived for two problems of infinite bonded dissimilar media, one with a semi-infinite crack and the other with a finite crack along the interface. The derived thermal weight functions are shown to reduce to the already known expressions of thermal weight functions available in the literature for the respective homogeneous elastic body. Using these thermal weight functions, the stress intensity factors are computed for the above interface crack problems when subjected to an instantaneous heat source.

Continuous Recording of Retardation and Intensity of Echoes from the Ionosphere

Pulse retardation method of Breit and Tuve has been modified to record continuously the equivalent height as well as the intensity of reflections from the ionosphere. Synchronized pulses are transmitted, and the received ground pulse and the reflected pulses, after amplification and suitable distortion, are applied to the focusing cylinder of a cathode ray tube the horizontal deflecting plates of which are connected to a synchronized linear time base circuit. The pattern on the screen is composed of a bright straight line corresponding to the time base with dark gaps corresponding to the received pulses. The distance between the initial points of the gaps represents retardation while the widths of the gaps correspond to the intensity of the pulses. The pattern is photographed on a vertically moving film. One of the first few records taken at Bangalore on 4 megacycles is reproduced. It shows, among other things, that the less retarded component of magneto-ionic splitting from the F layer is present most of the time. Whenever the longer retardation component does occur, it has stronger intensity than the former. Towards the late evening hours, just before disappearing, when the F layer rises and exhibits magnetoionic splitting, the intensity of the less retarded component is extremely low compared with the other component.

Enhancement of photoluminescence intensity by photoinduced interdiffusion in nanolayered a-Se/As2S3 films

Optical parameters of chalcogenide glass multilayers with 12–15 nm modulation lengths prepared by thermal evaporation can be changed by laser irradiation. Photoluminescence (PL) studies were carried out on such nonirradiated and irradiated multilayered samples of a-Se/As2S3 (sublayer thickness of a-Se is 4–5 nm for one set of samples and 1–2 nm for the other set. However As2S3 sublayer thickness is 11–12 nm for both sets of samples.) PL intensity can be increased by several orders of magnitude by reducing the Se well layer (lower band gap) thickness and can be further increased by irradiating the samples with appropriate wavelengths in the range of the absorption edge. The broadening of luminescence bands takes place either with a decrease in Se layer thickness or with irradiation. The former is due to the change in interface roughness and defects because of the enhanced structural disorder while the latter is due to photoinduced interdiffusion. The photoinduced interdiffusion creates defects at the interface between Se and As2S3 by forming an As–Se–S solid solution. From the deconvoluted PL spectrum, it is shown that the peak PL intensity, full width half maximum, and the PL quantum efficiency of particular defects giving rise to PL, can be tuned by changing the sublayer thickness or by interdiffusion.

Moderate intensity static magnetic field has bactericidal effect on E. coli and S. epidermidis on sintered hydroxyapatite

The application of electromagnetic field in the context of bacteria associated infections on biomaterial surfaces has not been extensively explored. In this work, we applied a moderate intensity static magnetic field (100 mT) to understand the adhesion and growth behavior of both gram positive (S. epidermidis) and gram negative bacteria (E. coli) and also to investigate bactericidal/bacteriostatic property of the applied electromagnetic field. An in-house built magnetometer was used to apply static homogeneous magnetic field during a planned set of in vitro experiments. Both the sintered hydroxyapatite (HA) and the control samples seeded with bacteria were exposed to the magnetic field (100 mT) for different timescale during their log phase growth. Quantitative analysis of the SEM images confirms the effect of electromagnetic field on suppressing bacterial growth. Furthermore, cell integrity and inner membrane permeabilization assays were performed to understand the origin of such effect. The results of these assays were statistically analyzed to reveal the bactericidal effect of magnetic field, indicating cell membrane damage. Under the investigated culture conditions, the bactericidal effect was found to be less effective for S. Epidermidis than E. coli. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2012:100B:12061217, 2012.

Intensity profile of light scattered from a rough surface

We present in this paper, approximate analytical expressions for the intensity of light scattered by a rough surface, whose elevation. xi(x,y) in the z-direction is a zero mean stationary Gaussian random variable. With (x,y) and (x',y') being two points on the surface, we have h. = 0 with a correlation, = sigma(2)g(r), where r = (x - x')(2) + ( y - y')(2)](1/2) is the distance between these two points. We consider g(r) = exp-r/l)(beta)] with 1 <= beta <= 2, showing that g(0) = 1 and g(r) -> 0 for r >> l. The intensity expression is sought to be expressed as f(v(xy)) = {1 + (c/2y)v(x)(2) + v(y)(2)]}(-y), where v(x) and v(y) are the wave vectors of scattering, as defined by the Beckmann notation. In the paper, we present expressions for c and y, in terms of sigma, l, and beta. The closed form expressions are verified to be true, for the cases beta = 1 and beta = 2, for which exact expressions are known. For other cases, i.e., beta not equal 1, 2 we present approximate expressions for the scattered intensity, in the range, v(xy) = (v(x)(2) + v(y)(2))(1/2) <= 6.0 and show that the relation for f(v(xy)), given above, expresses the scattered intensity quite accurately, thus providing a simple computational methods in situations of practical importance.